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TLbc IRural ZcxUJBoo\\ Series 

Edited by L. II. BAILEY 



SOILS 

THEIR PROPERTIES AND MANAGEMENT 



Edited by L. II. BAILEY 

li. 31. Dnggar, Plant Physiology. 

J. F. Duggar, Southern Field Crops. 

Gny, The Principles and Practice of 
Judging Live-Stock. 

Harper., Animal Husbandry for Schools. 

Hitchcock, A Text-book of Grasses. 

Livingston, Field Crop Production. 

Lyon, Pippin and Buckman, Principles of 
Soil Management. 

ManJi, Beginnings in Agriculture. 

Montgomery, The Corn Crops, 

Piper, Forage Plants and their Culture. 

Warren, Elements of Agriculture. 

Warren, Farm Management. 

Wheeler, Manures and Fertilizers. 

White, Principles of Floriculture. 

Widtsoe, Principles of Irrigation Prac- 
tice. 

Others in Preparation. 



SOILS 



THEIR PROPERTIES AND MANAGEMENT 



BY 
T. LYTTLETON LYON, Ph.D. 

PROFESSOR OF SOIL TECHNOLOGY, CORNELL UNIVERSITY 

ELMER 0. FIPPIN, B.S.A. 

EXTENSION PROFESSOR OF SOIL TECHNOLOGY 
CORNELL UNIVERSITY 

HARRY O. BUCKMAN, Ph.D. 

ASSISTANT PROFESSOR OF SOIL TECHNOLOGY 
CORNELL UNIVERSITY 



THE MACMILLAN COMPANY 
1915 

All rights reserved 






COPYEIGHT, 1909 AND 1915, 

By the MACMILLAN COMPANY. 
Set up and electrotyped. Published September, 1915. 



Noiioooti l^xnt 

J. S. Cashing Co. — Berwick & Smith Co. 

Norwood, Mass., U.S.A. 

SEP -9 1915 

^CI.A4114()8 

'k^' / » 



ACKNOWLEDGMENTS 

The authors wish to acknowledge the originals of 
the two colored maps as occuring in Bulletins 60 and 
96 of the Bureau of Soils, U. S. Department of Agricul- 
ture. The remaining illustrations were drawn es- 
pecially for this text. Some few are copies in part, or 
in whole, from other autliors. Acknowledgments not 
made in text are due the Bureau of Soils, U. S. De- 
partment of Agriculture ; T. C. Chamberlin ; E. W. 
Hilgard; F. H. King; G. P. Merrill, and H. W. Wiley. 
The authors wish also to express their appreciation to 
Messrs. A. B. Beaumont and J. H. Bromley for their 
careful work in the preparation of the original drawings 
and to Miss Lela G. Gross for aid on the manuscript. 
Thanks are also due Professor W. D. Bancroft for sug- 
gestions as to the theoretical phases of soil colloids 
and to Professor J. L. Stone for a like favor regarding 
the soundness of the chapter on fertilizer practice. 



TABLE OF CONTENTS 

CHAPTER I 

PAGES 

Some General Considerations ...... 1-12 

Composition of the soil, 1 — Factors for plant growth, 
2 — Plant food elements, 3 — Abundance of plant food 
elements, 4 — Soil-forming rocks, 5 — Soil-forming min- 
erals, 6 — Relative abundance of minerals, 7 — Organic 
matter, 8 — The soil and the plant, 9. 

CHAPTER II 

Soil-forming Processes 13-30 

Water, 10 — Wind, 11 — Ice, 12 — Heat and cold, 13 

— Frost, 1-4 — Plants and animals, 15 — Oxidation and 
carbonation, 16 — Deoxidation, 17 — Hydration, 18 — 
Solution, 19 — A general statement of weathering, 20 — 
Factors affecting weathering, 21 — Law of mineral and 
rock decay, 22 — Special cases of weathering, 23 — Prac- 
tical relationships of weathering, 24. 

CHAPTER III 

The Geological Classification of Soils . . . 31-45 

Residual soils, 25 — Distribution of residual soils, 26 

— Cumulose soils, 27 — CoUuvial soils, 28 — Alluvial 
soils, 29 — Distribution of alluvial soils, 30 — Marine 
soils, 31 — Characteristics of marine soils, 32 — Distri- 
bution of marine soils, 33, 

CHAPTER IV 
Geological Classification of Soils {Continued) . . 46-64 
The ice sheet, 34 — The American ice sheet, 35 — 
Cause of the ice age, 36 — The extension of the ice sheet, 
37 — The ice as a soil builder, 38 — Glacial till soils, 39 



viii TABLE OF CONTENTS 

PAGES 

— Composition of glacial soils, 40 — Humus of glacial 
soils, 41 — Glacial lakes, 42 — Lacustrine soils — glacial 
lake, 43 — Lacustrine soils — recent lake, 44 — JEo\'\a,r\ 
soils, 45 — Loess soils, 4G — Distribution of loess, 47 — 
Adobe soils, 48 — Sand dunes, 49 — Volcanic dust, 50. 

CHAPTER V 
Climatic and Geochemical Relationships of Soils . 65-82 
Climatic relationships, 51 — Geochemical relationships 
of residual and marine soils, 52 — Residual and glacial 
soils, 53 — Effect of glaciation on agriculture, 54 — Hu- 
mid and arid soils, 55 — Soil color, 56 — White and 
black soils, 57 — Red and yellow soils, 58 — Agricul- 
tural significance of color, 50 — Soil and subsoil, 60 — 
Soil and subsoil of humid regions, 61 — Soil and subsoil 
of arid regions, 62. 

CHAPTER VI 

The Soil Particle 83-107 

Soil separates and mechanical analysis, 63 — Princi- 
ples of mechanical analy.sis, 64 — Mechanical analysis 
by water in motion. Schone elutriator, 65 — Hilgard's 
churn elutriator, 66 — Yoder's centrifugal elutriator, 67 

— Mechanical analysis by water at rest — Osborne's 
beaker method, 68 — Atterberg's modified Appiani silt 
cylinder, (5!) — Centrifugal soil analysis, 70 — Classifica- 
tion of soil particles, 71 — Bureau of Soils classification, 
72 — Physical character of the separates, 73 — Mineral- 
ogical characteristics of the separates, 74 — The chem- 
ical constitution of soil particles, 75 — Value of a 
mechanical analysis, 76 — Soil class, 77 — Determination 
of class, 78 — The significance of texture and class, 79. 

CHAPTER VII 
Some Physical Properties of the Soil .... 108-125 
Arrangement of soil particles, 80 — The absolute spe- 
cific gi-avity of the soil, 81 — Apparent specific gravity, 



TABLE OF CONTENTS ix 

PAGES 

82 — Actual weight of a soil, 83 — Pore space in soil, 84 

— The number of soil particles, 85 — Surface exposed 
by soil particles, 86 — The effective mean diameter of 
soil particles, 87. 

CHAPTER VIII 

The Organic Matter of the Soil 126-152 

The source and distribution of organic matter, 88 — 
Composition of plants, 89 — Decay of organic matter in 
soils, 00 — Composition of soil humus, 91 — The work of 
Oswald Schreiner, 92 — Toxic material in the soil, 93 — 
End products of humus decay, 94 — Carbonized mate- 
rials of soil, 95 — The estimation of soil organic matter, 
96 — The estimation of soil humus, 97 — The organic 
content of representative soils, 98 — The humus content 
of soil, 99 — The influence of the original material on 
the resultant humus, 100 — Effects of organic matter on 
soil, 101 — Maintenance of soil organic matter, 102. 

CHAPTER IX 

The Colloidal Matter of Soils 153-169 

The colloidal state, 103 — The properties of colloids, 
104 — Colloidal phases, 105 — Flocculation, 106 — Com- 
mon soil colloids and their generation, 107 — Prepara- 
tion of colloids, 108 — Colloids and soil properties, 109 

— Factors affecting colloids, 110 — Estimation of col- 
loidal content, 111. 

CHAPTER X 

Soil Structure 170-197 

Plasticity, 112 — The cause of plasticity, 113 — The 
importance of plasticity, 114 — Cohesion, 115 — Methods 
of determining cohesion, 116 — Factors affecting cohe- 
sion, 117 — Moisture limits for successful tillage, 118 — 
Control of cohesion and plasticity, 119 — Soil tilth, 120 

— Granulation, 121 — Forces facilitating granulation, 
122 — Wetting and drying, 123 — Freezing and thawing. 



X TABLE OF CONTENTS 

PAGES 

124 — Addition of organic matter, 125 — Action of plant 
roots and animals, 126 — Addition of lime, 127 — Til- 
lage, 128 — The action of the plow, 129 — H^sum^, 130. 

CHAPTER XI 
The Forms of Soil Watek and tiieik Movement . . 198-242 
Methods of expressing soil moisture, 131 — Kinds of 
water in the soil, 132 — Hygroscopic water, 133 — Effects 
of texture and humus on hygroscopicity, 134 — Nature 
of the film, 135 — Effect of humidity and temperature 
on hygroscopic water, 13G — Determination of hygro- 
scopicity, 137 — Heat of condensation, 138 — Capillary 
water, 139 — Surface tension and the force developed 
thereby, 140 — The form of water surfaces between soil 
particles, 141 — Factors affecting capillary water, 142 — 
Surface tension and the amount of capillary water, 143 

— Texture and the amount of capillary water, 144 — 
Effect of structure on the amount of capillary moisture, 
145 — Organic matter and the amount of capillary mois- 
ture, 146 — Determination of capillary water, 147 — The 
moisture equivalent of soils, 148 — The maximum re- 
tentive power of soils, 149 — Capillary movement, 150 

— Factors affecting rate and height of capillary move- 
ment, 151 — Effect of thickness of film on capillary 
movement, 152 — Surface tension and capillary move- 
ment, 153 — Effect of texture on capillary movement, 
154 — Texture and capillary pull of soils, 155 — Effect 
of structure on capillary movement. 156 — Gravitational 
water, 157 — Pressure and the movement of gravity 
water, 158 — Effect of temperature on the flow of grav- 
ity water, 159 — Effect of texture and structure on the 
flow of gravity water, 160 — Determination of the quan- 
tity of free water that a soil will hold, 161 — The calcu- 
lation of the free water of a soil, 162 — Value of studying 
flow and composition of gravitational water, 163 — The 
study of gravity water by means of tile drains, 164 — 
The lysimeter method of studying gravitational water, 
165 — Thermal movement of water, 166. 



TABLE OF CONTENTS 



XI 



CHAPTER XII 

The Water of the Soil in its Relation to Plants 

Functions of water to the plant, 167 — The water 
requirement of plants, 168 — Factors affecting trans- 
piration, 169 — Effect of crop and climate on transpira- 
tion, 170 — Effect of soil moisture on transpiration, 171 
— Influence of fertility on transpiration, 172 — Effect of 
texture on transpiration, 173 — Actual amounts of water 
necessary to mature a crop, 174 — Role of capillarity in 
the supplying of the plant with water, 175 — Inliuence 
of water on the plant, 176 — Availability of the water in 
the soil, 177 — Unavailable soil water, 178 — The wilting 
coefficient of plants, 179 — Determination of the wilting 
point, 180 — Calculation of the wilting point, 181 — Re- 
lation of texture to the wilting point, 182 — Available 
and superavailable water, 183 — Optimum moisture for 
plant growth, 184. 

CHAPTER XIII 

The Control of Soil Moisture ..... 

Run-off losses, 185 — Percolation losses, 186 — Methods 
of checking loss by run-off and leaching, 187 — Evapo- 
ration losses, 188 — Methods of checking evaporation 
losses, 189 — Mulches for moisture control, 190 — Kinds 
of mulches, 191 — The functions of a mulch, 192 — The 
soil mulch versus the dust mulch, 193 — Formation of a 
mulch, 194 — Depth of a mulch, 195 — R^sumd of mulch 
control, 196 — AVater saved by a mulch, 197 — Effect of 
mulches other than on moisture, 198 — General useful- 
ness of a mulch, 199 — Other practices affecting evapo- 
ration losses, 200 — Fall and early spring plowing, 201 — 
Rolling, 202 — Shelters, 203 — Level cultivation, 204 — 
Plants, 205 — Summary of moisture control, 206. 



PAGES 

243-263 



264-288 



CHAPTER XIV 

Soil Heat .......... 

Relation of heat to germination and growth, 207 — 
Chemical and physical changes due to heat, 208 — 



289-326 



Xll TABLE OF CONTENTS 

PAOE8 

Sources of soil heat, 209 — Factors affecting soil tem- 
perature, 210 — Specific heat, 211 — Variations of spe- 
cific heat, 212 — Specific heat based on volume of soil, 
213 — Effect of water on specific heat, 214 — Absorptive 
power of soils for heat, 215 — Effect of color on absorp- 
tion of heat, 210 — Effects of texture and structure on 
heat absorption, 217 — Radiation of heat by soil, 218 — 
Conductivity and convection of heat in soils, 219 — 
Measurement of conductivity, 220 — Effect of texture 
on conductivity of heat, 221 — Effects of humus and 
structure on conductivity, 222 — Influence of moisture 
on heat conductivity in soil, 223 — Effect of evaporation 
of water on soil temperature, 224 — Effect of organic 
decay on soil temperature, 225 — Relation of slope to 
soil temperature, 226 — Heat supply and its effects, 227 

— Control of soil temperature, 228. 

CHAPTER XV 

Availability of Plant Nutkients as Determinkd by 

Chemical Analysis ...... 327-348 

Solubility of the soil in various solvents, 229 — Com- 
plete solution of the soil, 230 — Partial solution with 
strong acids, 231 — Significance of a strong hydrochloric 
acid analysis, 232 — Relation of texture to solubility, 
233 — Nature of the subsoil, 234 — Calcium carbonate, 
235 — Deficiency of ingredients and manurial needs, 230 

— Partial solution with weak acids, 237 — Advantages 
in the use of dilute acids, 238 — The one-per-cent citric 
acid method, 239 — Usefulness of the citric acid method, 
240 — Dilute mhieral acids, 241 — Extraction with an 
aqueous solution of carbon dioxide, 242 — Extraction 
with pure water, 243 — Influence of absorption, 244 — 
Other factors influencing extraction, 245 — The soil solu- 
tion in situ, 240 — Devices for obtaining a soil solution, 
247 — Composition and concentration of the soil solu- 
tion, 248 — Variability in composition and concentration 
of the soil .solution, 249 — Discussion of the theories 
regarding soil solutions, 260. 



TABLE OF CONTENTS xiii 

CHAPTER XVI 

PAors 
The Absorptive Properties of Soils .... 349-374 
Substitution of bases, 251 — Time required for absorp- 
tion, 262 — Insolubility of certain absorbed' substances, 
253 — Influence of size of particle, 254 — Causes of ab- 
sorption, 255 — Zeolites, 256 — Chabazite, 257 — Pres- 
ence of zeolites questioned, 258 — Ab.sorption of phos- 
phoric acid, 259 — Formation of insoluble phosphates, 
260 — Absorption, 261 — Absorption by colloids, 262 — 
Absoqitive properties of colloidal matter, 263 — Selective 
absorption, 264 — Absorptive power of colloidal silicates, 
265 — Absorption by colloids versus absorption by zeo- 
lites, 266 — Absorption by organic matter, 267 — Ab- 
sorption of water vapor and of gases by soils, 268 — 
Absorption of ammonia, 269 — Absorption of carbon 
dioxide, 270 — Absorption of nitrogen and oxygen, 271 

— Relation of temperature to gas absorption, 272 — 
Relation of absorptive capacity to productiveness, 273 

— Absorption as related to drainage, 274 — Substances 
usually carried in drainage water, 275 — Drainage rec- 
ords at Rothamsted, 276 — Drainage records at Brom- 
berg, 277 — Losses of nitrogen and calcium, 278 — 
Composition of surface water, 279. 

CHAPTER XVII 

Acid or Sour Soils 375-390 

Nature of soil acidity, 280 — Positive acidity, 281 — 
Negative acidity, 282 — Production of sour soils, 283 — 
Removal of bases by drainage as a cause for acidity, 284 

— Removal of bases by plants, 285 — Effect of green 
manures on acidity, 286 — Effect of fertilizers on soil 
acidity, 287 — Acidity in relation to climate and to for- 
mation of soil, 288 — Weeds that flourish on sour soils, 
289 — Crops adapted to sour soils, 290 — Crops that are 
injured by acid soils, 291 — Qualitative tests for acidity, 
292 — Litmus paper test, 293 — Ammonia test, 294 — 
Zinc sulfide test, 295 — Litinu.s paper and potassium 
nitrate, 296 — Acid test for carbonates, 297 — Plants as 



XIV 



TABLE OF CONTENTS 



indicators of acidity, 298 — Quantitative determinations 
of acidity, 299 — Potassium nitrate method, 300 — Lime- 
water method, 301 — R6sum6, 302. 



CHAPTER XVIII 

Alkali Salts ......... 

Composition of alkali salts, 303 — White and black 
alkali, 304 — Effect of alkali on crops, 305 — Effect on 
different plants, 30(3 — Other conditions that influence 
the action of alkali, 307 — Accumulation of alkali, 308 — 
Irrigation and alkali, 300 — Handling of alkali lands, 310 
— Eradication of alkali, 311 — Leaching with under- 
drainage, 312 — Correction with gypsum, 313 — Scraping, 
314 — Flushing, 315 — Control of alkali, 316 — Cropping 
with tolerant plants, 317 — Alkali spots, 318. 



391-403 



CHAPTER XIX 

Absorption of Nutritive Salts by Agricultural Plants 

How plants absorb nutrients, 319 — Relation between 

root-hairs and soil particles, 320 — Liebig and Sachs on 

solvent action of plant-roots, 321 — Czapek's experiment, 

322 — Secretion of an oxidizing enzyme by plant-roots, 

323 — Importance of carbon dioxide as a solvent, 324 — 
Insufficiency of carbon dioxide, 325 — The present status 
of the question, 326 — Possible root action on colloidal 
complexes, 327 — Why crops vary in their absorptive 
powers, 328 — Extent of absorbing systems, 329 — Os- 
motic activity, 330 — The absorptive power of cereals, 
331 — The feeding of grass crops, 332 — Leguminous 
crops, 333 — Root crops, 334 — Vegetables, 335 — Fruits, 
330 — Mineral substances absorbed by plants, 337 — Re- 
lation of plant growth to concentration of nutrient solu- 
tion, 338 — Quantities of plant food materials removed 
by crops, 339 — Quantities of plant food materials con- 
tained in soils, 340 — Possible exhaustion of mineral 
nutrients, 341. 



404-420 



TABLE OF CONTENTS 



XV 



CHAPTER XX 

Organisms in the Soil 

Macruorya7iisms. 

Rodents, 342 — Worms, 343 — Insects, 344 — Large 
fungi, 345 — Plant root, 346. 

Microorganisms. 

Plant microorganisms, 347 — Plant microorganisms 
injurious to higher plants, 348 — Plant microorganisms 
not injurious to higher plants, 349 — Bacteria, 350 — 
Distribution of bacteria, 351 — Numbers of bacteria, 352 
— Numbers as influenced by season, 353 — Conditions 
affecting gro^\•th, 354 — Oxygen, 355 — Moisture, 356 — 
Temperature, 357 — Organic matter, 358 — Soil acidity, 
359 — Functions of soil bacteria, 360 — Decomposition 
of mineral matter, 361 — Influence of certain bacteria 
and molds on the solubility of phosphates, 362 — Decom- 
position of non-nitrogenous organic matter, 363 — De- 
composition of nitrogenous organic matter, 364. 



PAGES 

421-442 



CHAPTER XXI 

The Nitrogen Cycle 

Decay and putrefaction, 365 — Ammonification, 366 — 
Bacteria and substances concerned in ammonification, 
367 — Nitrification, 368 — Effect of organic matter on 
nitrification, 369 — Effect of soil aeration on nitrification, 
370 — Effect of sod on nitrification, 371 — Depths at 
which nitrification takes place, 372 — Loss of nitrates 
from the soil, 373 — Nitrate reduction, 374 — Nitrate 
assimilating organisms, 375 — Denitrifieation, 376 — Ni- 
trogen fixation through symbiosis with higher plants, 
377 — Relation of bacteria to nodules on roots, 378 — 
Transfer of nitrogen to the plant, 379 — Soil inoculation 
for legumes, 380 — Nitrogen fixation without symbiosis 
with higher plants, 381 — Nitrogen-fixing organisms, 382 
— Mixed cultures of nitrogen-fixing organisms, 383 — 
Nitrogen fixation and denitrifieation antagonistic, 384. 



443-474 



xviii TABLE OF CONTENTS 

PAGES 

The lime-magnesia ratio, 458 — Forms of calcium, 459 — 
Caustic limes, 460 — Carbonate of lime, 461 — Relative 
effectiveness of caustic lime and carbonate, H')2 — Sul- 
fate of calcium, 463 — Common salt, 464 — Muck, 465. 

CHAPTEU XXV 

Fertilizer Practice 546-576 

Effects of nitrogen on plant growth, 466 — Effects of 
phosphorus on plant growth, 467 — Effects of potassium 
on plant growth, 468 — Law of the minimum, 469 — Fer- 
tilizer brands, 470 — Fertilizer inspection and control, 
471 — Trade values of fertilizers, 472 — The buying of 
mixed goods, 473 — Home-mixing fertilizers, 474 — Fer- 
tilizers not to be mixed, 475 — How to mix fertilizers, 
476 — Factors affecting the efficiency of fertilizers, 477 — 
Method and time of applying fertilizers, 478 — Fertiliz- 
ing crops, 479 — Systems of fertilization, 480. 

CHAPTER XXVI 

Farm Manures 577-618 

General character and function of farm manures, 481 
— Variable composition of manures, 482 — Litter, 483 — 
Class of animal, 484 — Individuality, condition, and age 
of animal, 485 — Food of animal, 486 — Handling of the 
manure, 487 — Composition and character of farm ma- 
nures, 488 — Actual plant-food in liquid and solid excre- 
ment, 489 ■'— Production of manure, 490 — Heiden's 
formula. 491 — Poultry manure, 492 — Commercial and 
agricultural evaluation of manures, 493 — The fermenta- 
tion of manure, 494 — Aerobic action, 495 — Anaerobic 
action, 496 — Fermentation in general, 497 — Gases from 
manures, 498 — Change of bulk and composition of rot- 
ting manure, 499 — Fire-fanging of manure, 500 — 
Waste of farm manures, 501 — Losses due to digestion, 
502 — Losses due to leaching and fermentation, 503 — 
Increased value of protected manure, 504 — The money 
waste of manure, 505 — Handling of manures, 506 — 
Care of manure in the stalls, 507 — Hauling directly to 



TABLE OF CONTENTS 



XIX 



the field, 508 — Cement pit, 509 — Covered barnyard, 
510 — Piles outside, 511 — Distribution of manure in the 
field, 512 — Reinforcement of manure, 513 — Benefits 
from reinforcing, 514 — Lime and manure, 516 — Com- 
posting, 516 — Manure and muck, 517 — Effects of ma- 
nure on the soil, 518 — Residual effect of manure, 519 — ■ 
riace of manure in the rotation, 520 — R^sum^, 521, 



CHAPTER XXVII 

Green Manures 

Effects of green-manuring, 522 — Quantities of plant 
constituents added by green-manuring, 523 — Decay of 
green manure, 524 — Crops suitable for green manures, 
525 — When to use green manures, 526 — When to turn 
under green crops, 527 — How to turn under green mate- 
rial, 528 — Green manures and lime, 529 — Green manure 
and the rotation, 630. 



619-626 



CHAPTER XXVin 
Land Drainage ......... 

Extent of drainage needed in humid regions, 531 — 
History of drainage, 532 — Effects of land drainage on 
the soil, 633 — Methods of drainage, 534 — Construction 
of small open ditches, 535 — Construction of large open 
ditches, 536 — Construction of early types of under- 
drains, 537 — Stone drains, 538 — Tile drains, 539 — 
Quality of tile, 540 — Shapes of tile, 541 — Protection of 
joints, 542 — Entrance of roots into tile, 543 — Protection 
of joints on curves, 544 — Foundation for tile, 545 — 
Arrangement of drainage systems, 546 — Grade of tile 
drains, 547 — Depth of drains, 548 — Distance between 
drains, 549 — Construction of drainage trenches for tile, 
650 — Laying tile, 651 — Size of tile, 652 — Amount of 
water to be removed from land, 653 — Carrying capacity 
of a tile-drain system, 554 — Cost of drainage, 555 — 
Storm channels, 556 — Silt basins, 657 — Surface intakes, 
558 — Outlets, 659 — Muck and peat soil, 560 — Drain- 



627-662 



XX 



TABLE OF CONTENTS 



age of ii'rigated and alkali lands, 661 — Vertical drainage, 
562 — Drainage by means of explosives, 563 — R^sum6, 
564. 

CHAPTER XXIX 

Tillage 

Objects of tillage, 565 — Implements of tillage, 566 — 
Effects on the soil, 567 — Classes of tillage implements, 
568 — Plows, 569 — Pulverizing action of the plow, 670 
— Types of plows, 571 — Shapes of moldboard plows, 
672 — Position of the furrow slice, 673 — Depth and 
width of furrow, 574 — Plow sole, 575 — Hillside plow, 
576 — Covering rubbish, 677 — Subsoil plow, 578 — 
Cultivators, 679 — Cultivators proper, 580 — Leveler 
and harrow types of cultivator, 581 — Seed cultivators, 
582 — Packers and crushers, 583 — Rollers, 584 — Clod 
crushers, 685 — Efficient tillage, 586. 



663-681 



CHA'PTER XXX 
Irrigation and Dry Farming 

Relation of irrigation to rainfall, 587 — Extent of irri- 
gated land, 588 — History of irrigation, 589 — Develop- 
ment of irrigation practice in the United States, 590 — 
Irrigation in humid regions, 591 — The Reclamation 
Service, 692 — Legal, economic, and social effects of 
irrigation, 593 — Divisions of irrigation, 594 — Source of 
water for irrigation, 505 — Canals, 596 — Preparation of 
land for irrigation, 597 — Methods of applying water, 
598 — Overhead sprays, 599 — Subirrigation, 600 — 
Methods most u.sed in arid regions, 601 — Flooding, 602 

— Furrows, 603 — Size and form of furrows, 604 — Unit 
of measurement, 605 — Amount of water to apply, 606 

— Time to apply water, 607 — Conservation of moisture 
after irrigation, 608 — Sewage irrigation, 609. 

Dry Farming. 

Practices in dry farming, 610 — Storage of water in 
the soil, 611 — Conservation of moisture, 612 — Alternate 
cropping, 613 — Drought-resistant crops, 614 — Soils 



682-717 



TABLE OF CONTENTS XXI 

PAGES 

associated with dry farming, (515 — Extent of dry fann- 
ing, 616. 

CHAPTER XXXI 

The Soil Survey 718-740 

The classification of soils by survey, 617 — Factors 
employed in classification, 618 — Texture, the soil class, 
619 — Special properties, the soil series,. 620 — Source of 
material, the soil group, 621 — Agency of formation, the 
soil province, 622 — Climate, 623 — The practical classi- 
fication of soils in the United States, 624 — The soil type 
and soil series, 625 — The equipment for survey work, 
626 — Procedure in the field, 627 — Collection of soil 
samples, 628 — The accuracy and detail of the soil sur- 
vey, 629 — The soil survey report, 630 — The soil map, 

631 — The extent of soil surveys in the United States, 

632 — Surveys by state institutions, 633 — Surveys in 
other countries, 634 — Use of the soil survey, 635. 



SOILS : THEIR PROPERTIES 
AND MANAGEMENT 

CHAPTER I 

SOME GENERAL CONSIDERATIONS 

The broken and weathered fragments of rock that 
cover in a thin layer the solid part of the earth and that 
furnish the foothold and, in part, the sustenance for plant 
life, are termed soil. Soil comes from rock and returns 
to rock. It is merely a transitory stage in the change 
from one form of rock to another. It is never still. From 
the time when the particle leaves the disintegrating rock 
until it is again cemented in the skeleton of the earth, 
it is subjected to almost constant movement and to the 
action of numerous forces that change it chemically and 
physically. It is the movement, the strain and the 
stress, the hard . treatment at the hands of disintegrating 
agencies, that make the soil useful to plant life. 

It was only the simpler forms of plants, however, that 
first throve on the pulverized rock. Tribe after tribe of 
plants has invaded the soil. Each has wrested from it 
the mineral matter necessary for its growth and develop- 
ment. Each has, in the end, left not only the mineral 
matter that it obtained from the disintegrated rock, but 
also the carbon and the oxygen that had been won from the 
B 1 



2 SOILS: PROPERTIES AND MANAGEMENT 

air in the struggle for life. Primitive plants have been 
followed by more highly organized ones as the incursions 
have gone on, and always to the profit of the soil, until 
the soil has accumulated a great store of organic matter 
and a teeming population of microscopic life. 

This debris of rock and plant residue that has accumu- 
lated through the centuries of struggle is the arable soil 
from which man obtains his bread. The study of this 
soil is a history of strife and struggle, and as the light of 
investigation is turned on it, new contestants, new opera- 
tions, new results, and new principles are brought to view 
and the story must be retold. 

1. Composition of the soil. — Broadly speaking, the 
soil is composed of two general classes of materials, rock 
and organic matter. The former usually makes up the 
bulk of the soil, while the latter occurs under normal 
conditions in relatively small amount^. In spite of this 
low proportion, however, its presence is of vital impor- 
tance to productivity. The soil has also three general 
phases — the physical, the chemical, and the biological. 
In the physical phase, the size and shape of particle, the 
movement of air and water, and other physical proper- 
ties are dealt with ; in the chemical phase, the composi- 
tion of the particle, of the organic matter, and of the soil 
solution is of dominant importance ; in the biological phase, 
the soil is seen to be not an inert material, but teeming 
with life — mmute forms of life, to be sure, but of great 
importance in the manufacture of food for plants. Under 
these three general phases, then, the changes going on m 
a soil may be studied, and they are found to be directed 
primarily toward the production and maintenance of con- 
ditions .favorable for plant growth. The soil is not a 
simple medium to study, but is extremely complicated 



SOME GENERAL CONSIDERATIONS 3 

for two reasons : first, because of the complicated nature 
of its two general constituents ; and secondly, because of 
the action and interaction of these constituents with each 
other. 

2. Factors for plant growth. — The growth and devel- 
opment of a plant are largely the result of tw^o sets of 
factors, the internal and the external. The former de- 
pends on the nature of the plant itself, the latter on its 
environment. The external factors of plant growth under 
normal conditions may be classified as follows : (1) me- 
chanical support, (2) air, (3) heat, (4) light, (5) water, and 
(6) food. With the exception of light, the soil supplies, 
either wholly or in part, all the conditions named. As 
a mere mass of ground-up rock with which are mixed 
varying quantities of decayed organic matter, the soil 
acts as a medium for root development and thereby pro- 
vides a foothold for the plant. Air, heat, and water are 
supplied as a consequence of the inherent physical condi- 
tion of a soil. The circulation of water serves to bring 
food into solution for absorption by the rootlets. Thus 
the two prime functions of the soil are realized — the 
supplying of plant-food and of a foothold for plant life. 

3. Plant-food elements.^ — While the physical condition 
of the soil has tremendous influence on plant growth, the 
food elements must first be considered, since their avail- 
ability is so closely related to the factors that function 
in soil formation. Ten elements are usually considered 
as absolutely necessary for plant growth. They may be 
classified as follows : — 

1 For a complete discussion of the plant-food elements as re- 
lated to the plant, see Russell, E. J. Soil Conditions and Plant 
Growth, Chapter II, pp. 30-46, New York Citv. 2d edition, 
1915. 



4 SOILS: PROPERTIES AND MANAGEMENT 

Elements obtained from Elements coming directly from * 

air or water the soil itself 

Carbon Nitrogen Magnesium 

Oxygen Phosphorus Iron 

Hydrogen Potassium Sulfur 

Nitrogen Calcium 

Carbon is obtained very largely by the plant directly 
from the air as carbon dioxide (CO2) ; while oxygen 
comes directly from the atmosphere or from water, which 
is also the source of at least a part of the hydrogen utilized 
in vegetative growth. The other elements, except in 
the case of leguminous crops, are taken wholly from the 
soil solution itself. 

While all these elements found in the soil must be 
available in order that plants may grow normally, only 
a very few ever become limiting factors. The three 
elements most likely to be lacking in a soil from a food 
standpoint are nitrogen, phosphorus, and potassium. 
They may be designated as the primary elements for 
plant growth. The other elements are usually present 
in amounts many times greater than will ever be needed 
by crops. Calcium, while necessary in large quantities 
in a soil, is largely an amendment, and very seldom may 
limit plant growth because of beiug in too minute quantity 
to supply the food needs of a crop. The liming of a soil 
is for other purposes than the supplying of calcium for 
plant nutrition. Sulfur is supposed, in certain soils, 
to limit plant growth because of its insufficiency, but 
ordinarily it is never found in a minimum quantity. 

Nitrogen exists in the soil largely as a portion of the 

• Sodium, silicon, and aluminium are found in plants, but are 
not essential to proper growth. 



SOME GENERAL CONSIDERATIONS 5 

partially or wholly decayed organic matter present therein. 
It is utilized by the plant ordinarily in the form of nitrate. 
The atmosphere, composed of four-fifths nitrogen by 
volume, has been the original source of this element; 
and through natural processes which are continually 
at work the nitrogen has been transferred to the soil. 
The encouragement of this natural fixation, thus draw- 
ing upon the great body of gas surrounding the earth, 
has become of great practical importance in agricultural 
operations. 

Phosphorus has its origin in the mineral apatite and 
exists in most soils largely as a tricalcium phosphate 
(Ca3(P04)2). In case of a lack of lime or of the presence 
of considerable quantities of humus, phosphorus may be 
present as ferric or aluminium phosphates or as organic 
phosphoric acid. Phosphorus is probably taken up by 
the plant as the mono- or di-calcic phosphate (CaH4(P04)2 
orCa2Ho(P04)o). 

The potassium of the soil exists largely in feldspar 
(K2O . AI2O3 . G 8102), in mica, or in hydrated aluminium 
silicates, which, while rather insoluble, supply potash 
to the soil solution in the bicarbonate, chloride, nitrate, 
or sulfate forms. It is from such compounds that the 
plant draws upon the soil for this element. 

4. Abundance of plant-food elements. — Having con- 
sidered the plant-food elements, especially those of primary 
importance, it is of interest to note their distribution in 
the earth's crust. Clarke ^ estimates the composition 
of the lithosphere, which makes up 93 per cent of the 
known terrestrial matter, as follows : — 



1 Clarke, F. W. Data of Geochemistry. U. S. Geol. Survey, 
Bui. 491, p. 33. 1911. 



SOILS: PROPERTIES AND MANAGEMENT 



Oxygen . . 


. 47.17 


Sodium . . 


. . 2.43 


Silicon . . 


. 28.00 


Potassium 


. . 2.49 


Aluminium . 


. 7.84 


Hydrogen 


. . .23 


Iron . . . 


. 4.44 


Carbon . . 


. .19 


Calcium . . 


. 3.42 


Sulfur . . 


. .11 


Magnesium . 


. 2.27 


Phosphorus . 


. . .11 



The briefest scrutiny of this table reveals the fact that 
the lighter elements are the more abundant in the earth's 
crust. The first four elements make up eighty-seven per 
cent, while the primary elements of plant growth either 
are lacking or are present only in very small quantities. 

5. Soil-forming rocks. — As has been stated, ordinary 
soil is made up largely of inorganic matter which is derived 
from ground-up rock material. Therefore, in any study 
of soil origin or formation, however cursory, the atten- 
tion must be directed toward geological conditions, not 
because of their mere geological interest but because of 
their ultimate bearing on soil fertility and crop growth. 
In the soil we expect to find, and do find, fragments of 
the commonest rocks, because those most exposed and 
those present to the largest extent at the earth's surface 
must be the ones to break down into soil. Therefore 
the commonest soil-forming rocks are the rocks that 
are met so commonly in the field. They may be classified 
broadly under three heads — igneous, sedimentary, and 
metamorphic. Some of the common types are as follows : 



Igneous 


Sedimentary 


Metamorphic 


Granite 


Limestone 


Schist 


Syenite 


Sandstone 


Gneiss 


Diorite 


Shale 


Marble 


Diabase 


Dolomite 


Slate 


Gabbro 




Quartzite 


Peridotite 







SOME GENERAL CONSIDERATIONS T 

The igneous rocks furnish material for the formation 
of the types constituting the other groups. They may 
be divided in a general way into two classes — one con- 
taining a high percentage of silica and some free quartz, 
the other having a medium or low silica content and no 
quartz. The former is designated as acid, and the latter 
as basic since it contains a high percentage of the alkalies 
and the alkaline earth minerals. Granite and gabbro 
are excellent examples, respectively, of these general 
groups of rock. 

The sedimentary rocks, formed from material derived 
from the igneous rocks, have been deposited usually 
under fresh- or salt-water conditions. The development 
of pressure has in many cases been instrumental in the 
consolidation of this material. The limestone and the 
dolomite deposited by precipitation may be expected 
to be comparatively soluble rocks. Shale is merely a 
more or less hardened clay, while sandstone varies ac- 
cording to the cementing material which serves to hold 
its sand grains together. This cement may be iron 
(Fe-aOa), calcium carbonate (CaCOs), or silica (SiOi). 

The action of heat, usually with pressure, on either 
igneous or sedimentary rocks, results in the third group, 
the metamorphic. Thus, granite on metamorphosis 
may form either a gneiss or a schist ; limestone or dolomite 
may form marble ; shale may form slate ; and sandstone 
may form quartzite. 

On examination, ordinary rock is found to be composed 
of one or more minerals. In other words, it is a mineral 
aggregate. The mineral, in turn, is a natural compound 
of approximately a constant chemical composition, usually 
displaymg a crystalline form and other well-defined 
physical properties. In order to illustrate the com- 



8 SOILS: PROPERTIES AND MANAGEMENT 

plication that may arise, the mineral composition of some 
common rocks is given below : — 

Granite — Quartz, orthoclase, and plagioclase with mica 
and hornblende. 

Syenite — Orthoclase and mica with hornblende and 
augite. 

Basalt — Plagioclase and hornblende or augite with 
apatite, pyrite, and mica. 

Peridotite — Olivine with augite, pyrite, mica, and horn- 
blende. 

Limestone — Calcium or magnesium carbonate with traces 
of silica and iron. 

Sandstone — Sand cemented with iron, silica, or calcium 
carbonate. 

This complex character of rocks has an important 
bearing on the question of soil formation, since the presence 
or absence of certain minerals may have considerable in- 
fluence on the physical or chemical characteristics of the 
resultant soil. It is the minerals, therefore, rather than 
the rocks themselves, that must be looked to in a study 
of the great mass of inorganic matter, some active and 
some inactive, which makes up the bulk of ordinary 
soils. The question of the composition of a soil thus 
becomes more intensely geologic as we proceed. 

6. Soil-forming minerals. — A great many minerals 
have been discovered, studied, and classified, but only a 
comparatively few occur hi any abundance in the normal 
soil. Nevertheless, it may be said that practically all 
soils contain all the common rock-forming minerals. 
This is to be expected, as fragments of practically all the 
common rocks go to make up an ordinary soil. The 



SOME GENERAL CONSIDERATIONS 



9 



following list will give some idea of the minerals normally 
present in soils : — 

COMMON SOIL-FORMING MINERALS 

1. Quartz . . Si02 

2. Orthoclase K2O . AI2O3 . 6 SiOz 

3. Plagioclase NasO . AI2O3 . 6 SiOa, CaO . AI2O3 . 2 SiOa 

or combinations 

4. Hornblende Chiefly Ca(MgFe)3Si40i2 with 

NazAlzSi^Oiz and (MgFe)2 . (AIFe)2 . 

Si20l2 

5. Augite . . Chiefly Ca]MgSi206 with (MgFe) 

(AlFe)2Si206 

6. Muscovite 2 H2O . K2O . 3 AI2O3 . 6 Si02 

7. Biotite . . (HK)2 (MgFe)2 (AlFe)2 (SiOOa 

8. Olivine . 2 (MgFe)O . Si02 

9. Serpentine 3 MgO . 2 SiOs . 2 H2O 

10. Epidote . H2O . 4 CaO . 3 (AlFe)203 . 6 Si02 

11. Apatite . 3 CasPaOg + (CaFU or (CaClg) or 

combinations 

12. Zircon . . Zr02 . Si02 

13. Chlorite . H4o(FeMg)23Ali4Sii309o 

14. Calcite . CaC03 

15. Dolomite . CaCOs . MgC03 

16. Gypsum . CaS04 . 2 H2O 

17. Talc . . H20.3Mg0.4Si02 

18. Hematite . Fe203 

19. Siderite . FeCOs 

20. Limonite . 2 Fe.O? . 3 H2O 

21. Kaolinite . 2 HoO . AI2O3 . 2 Si02 

22. Zeolites . Complex hydrated aluminium silicates of 

Ca, K, and Na as Philolite (CaK2N2) 
Al2Siio024 . 5 H2O 



10 SOILS: PROPERTIES AND MANAGEMENT 

There are certain of these minerals that merit especial 
attention because of particular attributes which they may 
impart to a soil. Quartz, for example, is very common 
in all soils, making up usually from 85 to 99 per cent of 
their composition. It is a makeweight material, how- 
ever, as it is used to a very slight extent by most plants ; 
but it adds a stability to the soil that perhaps the soil 
would not otherwise have, and this function is of con- 
siderable significance. Of greater importance from the 
plant-food standpoint are the feldspars, of which orthoclase 
is probably primary because it is the source and store- 
house of the soil potash. Acted upon by physical and 
chemical agencies, it slowly supplies the soil solution with 
potassium, which in turn nourishes the plant. The micas 
also may furnish considerable potash for crop growth. 
The plagioclase, instead of being rich in potassium, as 
the formula indicates, contain the more basic elements, 
calcium and magnesium, as also do the pyroxenes and 
amphiboles represented by augite and hornblende. Olivine 
and serpentine, also silicates, are particularly rich in 
magnesium. Practically all the phosphorus in the soil, 
either organic or inorganic, has had its origin in the 
mineral apatite ; yet this mineral is present in rocks and 
soil usually in very small quantities, making up not more 
than 0.6 per cent of the bulk of igneous rocks. ]\Iore- 
over it is a rather insoluble material. This fact, together 
with the small quantities occurring in soil-forming rocks, 
may account for the need of phosphorus in many otherwise 
fertile soils. 

Calcium, so important as a basic material in soil, may 
be supplied to a certain extent by other minerals besides 
those already named — calcite, dolomite, and gypsum 
being perhaps the most important, especially the calcium 



SOME GENERAL CONSIDERATIONS 11 

carbonate in either the crystalline or the amor- 
phous forms. Plenty of calcium in a soil tends not only 
to better physical conditions, but also to improve chemical 
reactions and biological activity. The iron of the soil 
minerals is of importance in its color relationships, for 
when oxidized to the hematite form a bright red may be 
imparted, while a yellow may result if limonite is pro- 
duced. Color has great significance in a general estimate 
of soil productivity and is always an important factor in 
soil identification and survey. The tendency of most 
iron compounds in the soil is toward the hematite or the 
limonite form when subjected to oxidation and hydration. 

Kaolinite is a product of rock decomposition and is 
considered to be of considerable importance in most clays 
or clay loams. It is almost always impure and in this 
form is designated as kaolin. Kaolin and the soil zeolites, 
which are hydrated aluminium silicates carrying chiefly 
calcium, sodium, and potassium, are really the end prod- 
ucts of rock decay and therefore are secondary minerals. 
Consequently they must always be considered in any 
study of soil formation or of soil utilization, particularly 
as they may serve to enrich the soil solution in plant-food 
held by them in physical and chemical combinations. 

7. Relative abundance of minerals. — D'Orbigny ^ pre- 
sents the following table as a result of his calculation on 
the distribution of certain minerals in the earth's crust : — 

Percentage Percentage 

Feldspars 48 Carbonates .... 1 

Quartz 35 Hornblende, augite, etc. 1 

INIica 8 All other minerals . . 2 

Talc 5 

1 Hall, A. D. The Soil, p. 16. New York City. 1907. 



12 SOILS: PROPERTIES AND MANAGEMENT 

This agrees in general with the distribution of these 
minerals in the earth's surface and accounts for their 
universal presence in all soils. 

8. Organic matter. — The minerals as listed account 
for all the elements of plant-food obtained from the 
soil except nitrogen, which, as already indicated, is found 
very largely locked up in proteid and other nitrogenous 
material. The incorporation of organic matter in any 
soil, either by natural or by artificial means, besides 
tending to better its physical condition also enriches 
it in its total, or gross, nitrogen content. Though this or- 
ganic matter is so necessary in a fertile soil, its addition 
and thorough incorporation occurs late in the process of 
soil formation. Through the agency of bacteria and 
other organisms the organic compounds are slowly sim- 
plified, new compounds are split off, and nitrogen is in- 
troduced into the soil solution mamly as nitrate, which 
is one of the principal forms in which it may be used by 
plants growing on the soil. 

9. The soil and the plant. — Observed from the agri- 
cultural standpoint, then, the soil becomes purely a 
medium for crop production. Its composition, both 
mineral and organic, is of vital importance in the further- 
ance of such a use. All the physical, chemical, and 
biological agencies become directed toward this end. 
The study of the soil and a better imderstanding of its 
function will allow the great class of landowners not 
only to increase their crops, and consequently their 
profits, but at the same time to maintain as far as possible 
the fertility of our greatest national resource. A rational 
study of the soil should ultimately lead to a study of 
conservation in its bearing both to present prosperity 
and to the welfare of posterity. 



CHAPTER II 
SOIL-FORMING PROCESSES 

After the first proper estimate of the relations between 
the crop and the soil, the next step is toward the mode of 
soil formation and the agencies concerned. As might be 
expected, this is a complicated problem from the fact 
that most rocks are so heterogeneous in their composition. 
The question becomes still further involved because of 
the many factors that are continually functioning in rock 
decay. This process of the breaking down of rock masses 
and their gradual evolution into soil is called weathering.^ 
Rock weathering may be defined specifically as the changes 
that rock masses imdergo due to the physical and chemical 
activities of atmospheric agents. Everything on the 
earth's surface is seeking a more stable condition, and 
therefore, from a geological standpoint, is continually 
changing. If a soil represents a more stable condition 
than the exposed rock, the rock slowly evolves toward 
the soil. Again, if a soil presents constituents not wholly 
stable, that soil will change by an elimination or an 
alteration of these components. The soil, then, is a 
geologic unit. It is a transition product from one con- 
dition to another. 

This weathering, which brings about such changes and 
is such a factor in the modifications of our topography, is 

' For a complete discussion of weathering, see Merrill, G. P. 
Rocks, Rock Weathering, and Soils. New York. 1906. 

13 



14 SOILS: PROPERTIES AND MANAGEMENT 

very superficial and affects the earth to but relatively 
shallow depths. However, from the fact that it provides 
a medium for crop growth and at the same time is largely 
instrumental in maintaining the fertility of this medium, 
its agencies and processes become of great significance. 

The forces of weathering, while very diverse not only 
as to action but also as to product, permit of an outline 
so clear that the true relationships at once become ap- 
parent. This classification may be made mider two 
heads, mechanical and chemical, as follows : — 

Forces of weathering 

I. Mechanical* changes, or disintegration 

A. Erosion and denudation 

Water, wind, ice 

B. Temperature 

Heat and cold, and frost 

C. Plants and animals 

n. Chemical changes, or decomposition 

A. Oxidation and carbonation 

B. Deoxidation 

C. Hydration 

D. Solution 

10. Water. — The three great agencies of erosion and 
denudation are water, wind, and ice. They are instru- 
mental not only in the breaking up of rocks, but also in 
transporting the resultant materials. Water is especially 
of importance, as its denuding effects are very rapid when 
viewed over geological periods. It is estimated that 
the United States is being planed dowTi at the rate of 
one inch in seven hundred and sixty years. This is rapid 
enough to dig the Panama Canal in seventy-three da}s. 



SOIL-FORMING PROCESSES 15 

The water, in order to be a successful cutting agent, must 
be laden with sediment, so that its carrying power largely 
determines its power of erosion. In other words, it must 
be armed. 

From the time when the raindrops beat down on a 
surface until they have been gathered into rivulets and 
streams and finally discharged into the ocean, they are 
engaged in moving the detrital matter already produced. 
The jMississippi River is working fast enough at the 
present time to reduce the continent of North America 
to sea level in four million years. The Appalachian 
IMountams, born in Paleozoic times, have lost vastly 
more material than now remains for us to view. Our 
river and lake soils are due to the cutting and carrying 
power of the streams. The deltas, and the marine soils 
of the Atlantic and Gulf coasts, afford other examples 
of such effects. The continual pounding and grinding 
of waves are no mean factor in rock disintegration. The 
rounding of the sands is a mute evidence of this great 
force. 

11. Wind. — The wind as a soil-forming agent has, 
like water, two phases of action — erosive and transpor- 
tive. Sweeping over the land in dry weather, it has the 
power of picking up innumerable fine particles which 
may abrade rocks very noticeably over a term of years. 
The fluting of exposed rocks, especially in arid regions, 
the undermining of cliffs, and the polishing of stones 
to a smoothness equal to that of glass, are frequent occur- 
rences. The roughening of windowpanes in houses near 
the seashore during severe storms, and the illegibility 
of old tombstones, are of common record. Great areas 
of soil have been deposited by winds, especially in the 
United States. Tlie loess of the Mississippi Valley and 



16 SOILS: PROPERTIES AND MANAGEMENT 

the adobe of the Southwest owe their origin, at least 
partially, to the carryino; power of wind at a time when 
aridity existed over all this area. 

12. Ice. — When in large bodies, as in glaciers, ice 
exerts a tremendous grinding power. Glacial ice, by its 
mobility and motility, adapts itself to all topography, 
and as it moves slowly forward it grinds and scours and 
abrades even the hardest rocks. The great masses of 
pebbles and rocks which are picked up and imbedded 
by glaciers, especially in their lower surfaces, increase 
their cutting power many fold. The effect of glaciers 
is of particular interest because of the fact that all of 
the northern part of the United States was covered at 
one time with a great ice sheet, and our northern soils 
are due either directly or indirectly to the advances and 
retreats of this ice sheet. Formed in northern latitudes 
due to a change in climatic conditions, the ice sheet 
slowly covered many thousands of square miles of terri- 
tory, and as the ice was usually several thousand feet 
thick, hills, and often mountains, were overridden. Their 
tremendous weight made the grinding action almost 
irresistible. In the retreat, or melting back, of the ice, 
a mantle of this ground-up and well-mLxed material was 
deposited as soil ; while the streams flowing from its 
front, or into glacial lakes, were furnished with heavy 
sediments for distribution in other regions. 

13. Heat and cold. — The changes in temperature of 
the air, and the soils and rocks, tend vastly to augment 
the effect of the denuding agents. Constant expansion 
and contraction is productive of weakness and ultimate 
physical breakdown. Ileat is conducted slowly through 
rocks, thus leading to differential heating and unequal 
expansion or contraction. Rocks, as already noted, are 



SOIL-FORMING PROCESSES 17 

usually mineral aggregates, and these minerals vary 
in their coefficients of expansion. With every change 
of temperature, differential stresses are set up which 
ultimately must produce a considerable effect. When 
the separate minerals expand they expand differently, 
and when they contract they never again assume quite 
their former relationships to one another. Thus crevices, 
cracks, and rifts are created in rocks, especially those of 
heterogeneous mineral composition. The expansion coef- 
ficient of granite is .0000048 of an inch to a foot for every 
degree Fahrenheit, while that of marble is about .0000056 
of an inch. This seems to be very slight, but it must be 
remembered that under natural conditions large surface 
areas of rock are concerned. A sheet of granite 100 feet 
long will expand one-half an inch with a change of 75° 
Fahrenheit, which is not an uncommon variation of 
temperature in arid regions or high altitudes. This 
leads to chipping, flaking, and exfoliation. The rock 
fragments may range from microscopic sizes to large 
blocks, which are often split off with great violence. 

14. Frost. — Great as is the action of a simple change 
of temperature, its effects become many fold more ap- 
parent when water is present. We then have the action 
of frost. The cracks and crevices made by heat and cold 
will in a humid region become filled with water. This 
moisture, on freezing, exerts a very great force. The 
expansive power of water passing from the liquid to the 
solid state is equal to about 150 tons to a square foot, 
which is equivalent to the weight of a column of rock 
about a third of a mile in height. Moreover, most rocks 
contain a certain amount of water in themselves. This 
water is recognized in excavation operations as quarry 
water. The passage of the quarry water to a solid state 
c 



18 SOILS: PROPERTIES AND MANAGEMENT 

must result most disastrously to the physical condition 
of the rock. This action of frost is by no means com- 
plete when the rock is fined mechanically to a soil, but is 
continued on the soil itself. Such further fining is of 
the greatest importance in bettering the physical condi- 
tion of the soil, and is usually designated as a wetting and 
drying and freezing and thawing process. It is to such 
forces, more than to any other action, that the farmer 
owes the good tilth of his soil. 

15. Plants and animals. — Plants and animals unite 
their forces with those already mentioned to bring about 
further physical change. Unlike the modifications due to 
erosion, denudation, and temperature, these agencies affect 
the soil to a greater extent than they affect the parent rock. 
In other words, they begin their work after the minerals 
have been reduced, at least i)artially, to the form of a 
soil. Simple plants, as mosses and lichens, will develop 
readily on rock ledges and coarse rock fragments. They 
send their rootlets into the crevices and exert a prying 
and loosening effect. They also catch dust, provide 
humus, and gradually accumulate a soil in which higher 
and still higher species of plants may grow. Their 
chemical effects, especially regarding solution and oxida- 
tion, aid in this disintegration. The distribution of 
organic matter through the soil by the extension and 
death of plant roots is of no mean importance in soil 
fertility. Bacteria also may be a factor in rock decay, 
not only through their action on the humus material 
but also through a direct attack on the rocks themselves. 
Their nifluence, however, is probably mostly chemical. 

Animals also effect the fining of rock fragments and 
soils, from their burrowing and mixing tendencies. Such 
rodents as gophers and squirrels open up the soil, thus 



SOIL-FORMING PROCESSES 19 

providing better circulation of air and water. This 
brings about a deeper and more effective action of the 
other physical agencies of weathering. Earthworms 
produce similar effects. Their holes provide channels 
for ready drainage, and large quantities of soil are brought 
to the surface yearly by them. Darwm estimates that 
this amounts to as much as one or two inches in a 
decade. 

16. Oxidation and carbonation. — The physical and 
chemical forces do not act alone, but, as a general thing, 
combine in their effects. Thus one set of factors aids 
and accelerates the other. Scarcely has the disintegration 
of a rock begun, then, before its decomposition is also 
apparent. Of the chemical forces oxidation is usually, 
especially near the surface of the earth, the first to be 
noticed. It is perceptibly manifested in rocks carrying 
iron, and consists in such a change that the added oxygen 
may be accommodated. Sulfides readily succumb and 
become oxides, while these same oxides are prone to take 
up ox>'gen to their fullest extent. This oxidation is dis- 
closed by a discoloration of the rock, which is first streaked 
and stained with iron oxide but at last changed to a 
uniform ochre. The change may be exemplified by the 
following reactions : — 

2FeS2 + 7O2 + 4H2O = 2FeO + 4H2S04 
4 FeO + O2 = 2 FesOs (red) 

While not all the minerals contain iron, enough of them 
do to impart a fatal weakness to most rocks. The ferrous 
oxide (FeO), being soluble, is washed out and the rock is 
creviced and crumbled. A way is now open for more 
energetic physical and chemical decay. 

With the oxidizing action there is also the influence of 



20 SOILS: PROPERTIES AND MANAGEMENT 

carbon dioxide (COo), which is universally a constituent 
of air and is a product of the decaying vegetable matter 
present in most soils. This means that the water cir- 
culating among rock fragments, especially those of a soil, 
is heavily charged with this compound. The carbona- 
tion may be illustrated as follows : — • 

2 FeS2 + 7 O2 + 4 H.,0 + 2 CO2 = 2 FeCOg + 4 II2SO4 or 
2 NaOH + COo = NaoCOa + H2O 

17. Deoxidation. — Deoxidation is an opposite re- 
action to oxidation, being a loss of oxygen either to the 
air or to some other compound. With hematite it might 
take place as follows : — 

2 FezOa - O2 = 4 FeO 

Under normal conditions, however, it is not a very im- 
portant factor, since most rock fragments and soil are 
fairly well aerated, at least too well aerated to allow this 
reverse process to occur. In poorly drained soil or in 
soil very rich in humus and carrying organic acids it 
may occur, and is usually manifested by the development 
of })lue and gray colors, indicating that a reduction has 
taken place. The bleaching of sands, sandstones, and 
clays may be due partially to this, and also to a removal 
of the ferriferous salts in solution. Some subsoils dis- 
play this phenomenon. The a\'erage farmer, however, 
need not concern himself with the injuries that may re- 
sult from deoxidation. 

18. Hydration. — Hydration usually accompanies oxi- 
dation, but when occurring at great depths it may be 
practically the only change the minerals have undergone. 
Minerals, especially feldspars, become clouded and lose 
their luster on this assumption of chemically combined 



SOTL-FOEMING PROCESSES 21 

water. There is also a considerable increase in bulk, this 
being often as much as 8S per cent during the transition 
of a rock to a soil. Hydrated minerals, while apparently 
sound, quickly succumb when exposed to forces of weather- 
ing which are more superficial in their effects. Car- 
bonation and oxidation usually take place as correla- 
tive actions with hydration. A simple example of 
hydration is shown in the change of hematite to limo- 
nite, which occurs in practically every case when iron 
is allowed to oxidize from pyrite or a simpler oxide to 
the higher forms : — 

2 FesOs (red) + 3 HoO = 2 FesOs . 3 H.O (yellow) 

19. Solution. — As it is now quite evident that weather- 
ing, especially the chemical manifestations, is largely a 
simplification of compounds, and that water is almost 
universally present, some solution must occur. These 
simple materials are particularly prone to enter solution 
because of the presence of carbon dioxide, which, by 
acidifying the soil water, intensifies its solvent action to 
a considerable extent and consequently increases its power 
as a weathering agent. The atmosphere contains amounts 
of this gas ranging from 3.87 to 4.48 parts in 10,000, 
while considerable amounts are brought down on the 
rocks and the soil in snow and rain. The carbon dioxide 
evolved directly into the soil water from decaying organic 
matter also aids in keeping the soil charged with this gas. 
This means, then, that solution is largely a process of 
carbonation, especially after the soluble constituents have 
been thrown out into the soil solution. It is evident 
that oxidation, carbonation, hydration, and solution act 
in unison to bring about the chemical decay of the rock 
and the soil. This combined action may be represented 



22 SOILS: PROPERTIES AND MANAGEMENT 

by showing the various stages that orthoclase may undergo 
in producing a residual clay : — 

KAlSiaOs + HOH = HAlSi308 + KOH 

2 KOH + CO2 = K2CO3 + H2O 
HAlSiaOs - 2 Si02 = HAlSi04 (kaolinite) 

The silica in this case may become quartz or colloidal 
silica, or, what is more probable, may miite with certain 
elements to produce complex hydrated silicates. 

20. A general statement of weathering. — The question 
of rock weathering is complicated because no one action 
can be considered alone. All forces are acting together, 
tending to produce a great complex of reaction and inter- 
action. No amount of explanation or speculation can 
ever fully clarify the question as to the formation of a 
soil from a parent rock. Nevertheless, knowing in general 
the separate forces and reactions produced, we may formu- 
late the phenomenon in a general and superficial way. 
The change that a rock imdergoes in the formation of a 
residual clay is first a physical breaking-down accom- 
panied by chemical changes, which consist in the hydra- 
tion of the feldspars, the oxidation of the iron, and the 
solution and carbon ation of the soluble bases. 

21. Factors affecting weathering. — It is readily to be 
seen that the activity of the various agencies of weather- 
ing will be modified by certain factors which determine 
not only the kind of rock decay but also its rate. Of 
these, climate is probably of the greatest importance. 
The difference in the weathering in an arid region as 
compared to that in a humid region will illustrate this 
point. Under arid conditions the physical forces will 
dominate and the resulting soil will be coarse. Freezing 
and thawing, heat and cold, the action of the wind, and 



SOIL-FORMING PROCESSES 23 

the effect of animals, will be almost the sole agents. 
In humid regions, however, the forces are more varied 
and practically the full quota will be at work. Chemical 
decay will accompany the disintegration, and the resultant 
product will be finer and more minutely divided. The 
separate minerals will show also the change of color and 
loss of luster due to the decomposition of some of their 
essential elements. The same rocks, then, will behave 
differently under different climatic conditions. A granite, 
for instance, is a very insoluble rock as compared with a 
limestone, and in a humid region where chemical agencies 
are dominant it would be markedly more resistant. If, 
however, these two rocks are placed under arid conditions 
where the physical forces are potent, particularly as re- 
gards change of temperature, the comparison is different. 
The limestone, being homogeneous, is not affected by 
atmospheric changes ; but the stresses set up in granite 
due to differential contraction and expansion must ulti- 
mately reduce it to fragments. 

As weathering is confined to the very surface of the 
earth, the exposure or position of a rock will determine 
the kind and the rate of decay. If the rock is very deep 
below the surface, only hydration may occur ; while if 
it exists as an exposed ledge, the full force of the weather- 
ing agents will be sustained. If the debris of the decayed 
rocks is not removed, this serves as a blanket for the 
protection of the rocks below. The transportive powers 
of weathering are important in maintaining a clean sur- 
face for action. 

The texture of the rock is also a factor. Other things 
being equal, a coarsely crystalline rock will disintegrate 
and decompose more rapidly than one of finer grain. 
The coarser the grain, the larger the amount of interstitial 



24 SOILS: PROPERTIES AND MANAGEMENT 

space and the greater the encouragement to physical 
agencies. As physical changes open the way for chemical 
decay, coarse texture will ultimately encourage decomposi- 
tion as well as disintegration. 

Lastly, the disruptive forces of the rock will be in- 
fluenced by the chemical composition of the minerals 
and the mineral composition of the rock. A rock made 
up of minerals that offer but little resistance to decay 
will naturally succumb readily and quickly to a soil. 
Rocks that very largely bear minerals which are re- 
fractory in their nature, however, may never decompose 
far enough or rapidly enough to give a soil of any agri- 
cultural significance. The next step, then, in the study 
of soil formation is a consideration of the relative resistance 
of the minerals and the rocks. 

22. The law of mineral and rock decay. — ■ Considerable 
work has been done on the comparative solubility of 
minerals both in pure and carbonated water, but in most 
cases it has proved somewhat inconclusive. Neverthe- 
less we are able, by consulting the work of Midler,^ Clark,^ 
Daubree,^ and others, to arrange some of the commoner 
minerals in the order of their solubility, the most resistant 
minerals heading; the list : — 



1. 


Quartz 


6. 


Epidote 


11. 


Apatite 


2. 


Muscovite 


7. 


Serpentine 


12. 


Olivine 


3. 


Biolite 


8. 


Talc 


13. 


Calcite 


4. 


Orthoclase 


9. 


Hornblende 






5. 


Plagioclase 


10. 


Augite 







1 Miiller, R. Solution of Rocks in Carbonated Water. Jahrb. 
k-k Geol. Reichsanstalt, Vol. XXVII, p. 25. 1877. 

2 Clark, F. W. Data of Geochemistry. U. S. Geol. Survey, 
Bui. 330, p. 401. 1908. 

' Daubroc, A. Solubility of Orthoclase. Etudes de Geol. 
Experimentale, pp. 27 and 252. Paris, 1847. 



SOIL-FORMING PROCESSES 25 

The next step is to deduct some general law which can 
be shown to govern the resistance of these minerals. 
Such a statement would aid considerably in the making of 
general deductions regarding weathering. The siliceous 
content of some of these minerals, taken in the order as 
above, throws considerable light on this phase : — 

Per cent of SiOo Per cent of Si02 

Quartz 100 Hornblende .... 45 

Orthoclase .... 65 Olivine 41 

Plagioclase .... 55 Calcite trace 

Another case might be cited in a comparison of the 
chemical composition of anorthite, hornblende, and 
olivine : — 

Anorthite . CaAl2Si208 

Hornblende . Ca(MgFe).(Si03) with {(^tHSlsTo! 

Olivine . . (MgFe)2Si04 

It is to be noted that immediately as the resistance of a 
mineral declines, its content of silica decreases and the 
percentage of the basic constituents increases. Silica 
and aluminium, then, mark resistance to decay ; while 
calcium, magnesium, sodium, potassium, and iron func- 
tion in increasing susceptibility to decay. The law of 
mineral resistance may be formulated as : " The more 
basic a rock becomes, the more rapid is its decomposi- 
tion ; and the more acid, the less marked is its decay." ^ 

This general law certainly should apply to rocks that 
are made up of the minerals listed above. One example 
will show this clearly. The igneous rocks, as already 
stated, may be divided into two groups, acid and basic. 

1 Buekman, H. O. The Formation of Residual Clay. Trans. 
Amer. Ceramic Soc, Vol. XIII, p. 362. February, 1911. 



26 



SOILS: PROPERTIES AND MANAGEMENT 



This acidity and basicity is determined by the presence 
of siHca and the alkahes, respectively, as carried by 
certain essential minerals. Suppose we name some 
representative igneous rocks in the order of their acidity, 
and list some of the minerals carried by them : — 

1. Granite . . Quartz, orthoclase, and mica 

2. Diabase . . Plagioclase, mica, hornblende, or augite 

3. Peridotite . Principally olivine 

It is to be seen that the minerals contained by granite 
are more resistant than those carried by either the diabase 
or peridotite, while the olivine of the last group is near 
the foot of the list when the minerals are arranged in the 
order of their resistance. 

The following data ^ bear out the argument presented 
above as to the relative resistance of rocks : — 

Proportional Amounts of Fresh Rocks Soluble in Boil- 
ing Hydrochloric Acid and Sodium Carbonate Solutions 





Phonolite 


Diabase 


Granite 


Si02 

AljOsFeaOa 

CaO 

MgO 

K2O 


21.64 

12.60 

1.07 

.40 

.28 

5.45 


10.85 

15.65 

3.09 

2.20 

1.21 

.50 


9.49 

8.36 

.60 

.71 

1.68 


NajO 


1.23 




41.44 


33.50 


22.07 



It is evident, then, that the law of mineral resistance 
applies to rocks as well as to the separate minerals, al- 
though its application thereto is much more complex 
and difficult to interpret. 

' Merrill, G. P. Rocks, Rock Weathering, and Soils, p. 366, 
New York. 1906. 



SOIL-FORMING PROCESSES 



27 



23. Special cases of weathering. — The weathering of 
granite and Hmestone under different chmatic conditions 
has already been compared. The changes that take 
place in these rocks as they are evolved to residual clays 
may now be considered. The following analyses serve 
to show on what elements the losses are likely to be most 
serious during the process : — 

Fresh Granite and its Resultant Clay^ 



SiOa . 
AI2O3 . 
FeoOa . 
CaO . 
MgO. 
K2O . 
NaoO . 
P2O5 . 
Ignition 



Rock 



60.69 

16.89 

9.06 

4.44 

1.06 

4.25 

2.82 

.25 

.62 



Clay 



45.31 

26.55 

12.18 

00.00 

.40 

1.10 

.22 

.47 

13.75 



Percentage 
Lost 



52.45 
00.00 
14.35 
100.00 
74.70 
83.52 
95.03 
00.00 
Gain 



Virginia Limestone and its Residual Clay ^ 



Rock 



Clay 



Percentage 
Lost 



Si02 

AI2O3 

Fe203 

CaO 

MgO 

K2O 

Na20 

P2O5 

CO2 

H2O 



7.41 

1.91 

.98 

28.29 

18.17 

1.08 

.09 

.03 

41.57 

.57 



57.57 
20.44 

7.93 
.51 

1.21 

4.91 
.23 
.10 
.38 

6.69 



27.30 
00.00 
24.89 
99.83 
99.38 
57.49 
76.04 
68.78 
99.15 
Gain 



1 Merrill, G. P. Bui. Geol. Soe. Amer., Vol. 8, p. 160. 1879. 

2 Diller, J. S. U. S. Geol. Survey; Bui. 150, p. 385. 1898. 



28 



SOILS: PROPERTIES AND MANAGEMENT 



Soils have resulted in both cases from the decay of 
these rocks. In the case of the granite the resulting soil 
was a deep red clay, with quartz grains present. The 
soil from the limestone was a plastic clay, high in silica 
and aluminium. Leaching has probably gone on to a 
very great extent in both soils. It is noticeable also 
that the basic constituents have suffered the greatest 
losses, especially calcium, magnesium, sodium, and 
potassium. The carbonate has almost wholly disap- 
peared from the limestone clay, showing that a limestone 
soil may not necessarily be rich in lime. As a matter of 
fact, the chances are that if it is residual it will be lacking 
in that compound. When shown diagrammatically (See 
Figs. 1 and 2), the changes that the parent rocks have 
undergone chemically in forming a clay will become 
apparent. 





il 






>^^ 


o. 






















\ 


A 






s. 










\ 




K:( 


/ 


\. 


%0 


j 


\ 


< 








\ 






/v. 







/ 




\ 








\ 












/ 




/ 




















\ 


/ 


(SJ 






s 


y 




(aj/re^/f roc/C 


1 


/ 








J^ 


1^ 




(tja 


/^y 













FiQ. 1. — Diagrammatic representation of the chemical composition of 
fresh granite and its residual clay. See analyses above. 



SOIL-FORMING PROCESSES 



29 



As shown by the diagrams, the soil from the granite does 
not differ greatly from the original rock, except in loss 
of bases, assumption of water, and increase of organic 



































J 


v_ 








1 


\ 






■ 




~M 


\, 


/ 


y 




/ 


\ 
















\/ 






/ 


\ 
















,^/ 


^^ 




/ 




\ 














\ 


/ 








> 


(c^/re^ roc/C 




K^( 


,/ 


\ 


r^o 


s 


/ 


^y 


fm 


?5/c/a 


a/o 


be/ 






4 


9 




< 







Fig. 2. — Diagram showing the chemical composition of Virginia lime- 
stone and its residual clay. See analyses above. 



matter. The residual clay from the limestone presents 
greater differences, due to the almost entire disappear- 
ance of calcium carbonate. The diagrams for the two 
clays resemble each other fairly closely in spite of their 
widely differing sources. Because weathering causes 
the persistence and accumulation of silica, aluminium, 
and iron, and a loss of the basic materials, all soils as 
they weather tend to approach a similar composition. 
Yet, owing to a difference in the adjustment of the forces 
at work and in the time element, no two soils will ever 
be exactly alike. Soils will differ, then, from the original 
rock and from one another according to the intensity 



30 SOILS: PROPERTIES AND MANAGEMENT 

and character of tlie weathering and the constitution of 
the parent minerals. 

24. Practical relationships of weathering. — Weather- 
ing processes result in a general simplification of com- 
pounds. Their action first affects the rock, with the 
result that a soil is produced ; but they still remain ac- 
tive in the soil after it is in a condition to support plants. 
The physical agencies especially tend to loosen and fine 
the soil, contributing largely to its tilth. The farmer 
encourages such influences by plowing his land and by 
other operations. Were it not for such weathering 
action, the soil would become physically unable to afford 
foothold for plants. The continued chemical changes 
resulting in solution and carbonation provide a soil water 
rich in plant-food nutriment. Weathering, then, by a 
slow process over geologic periods has provided us with 
soil, and by the same slow process is maintaining the 
fertility of this creation. The encouragement and control 
of such an agency is of no small importance in agricultural 
practice. 



CHAPTER III 
THE GEOLOGICAL CLASSIFICATION OF SOILS 

Weathering must be considered as affecting soils both 
in situ and in motion. This gives two general classes of 
materials — those that have not been shifted far from 
their place of origin, and those in the formation of which 
the transporting agencies have been instrumental. These 
two general groups, designated as sedentary and trans- 
ported/ are subject to considerable subdivision, as 
follows : — 

o 1 ^ \ Residual 
Sedentary j ^^^^^^^ 

Gravity — Colluvial 

[ Alluvial 
Water s jNIarine 
Transported ] [ Lacustrine 

Ice — Glacial 
Wind — iEolian 

25. Residual soils. — This group of soils covers wide 
areas of our arable regions and comes from many kinds of 
rocks. Residual soils are old soils, the oldest with which 
we have to deal in agricultural operations. Since a 

1 See Trowbridge, A. C. A Classification of Common Sedi- 
ments. Jour, of, Geol., Vol. 22, No. 4, pp. 420-436. 1911. 

31 



32 



SOILS: PROPERTIES AND MANAGEMENT 



residual soil is formed in situ, the rocks that underlie it, 
if sound, show the character and composition of the rocks 
from which the soil was actually a product. In such 
soils the changes that a rock undergoes in forming a 
residual clay are to be studied to the best advantage. 
An examination of the various grades of material that are 
found overlying the country rock (Fig. 3) in an area where 







Fig. 3. 



The gradual transition of country rock into residual soil by 
weathering in situ. 



this residual mantle exists, reveals more or less accurately 
the gradations from rock to soil. Residual soils, besides 
being old soils, are usually nonstratified and present a 
heterogeneous mass of material. Since they have been 
subjected to leaching over vast periods, a very large 
amount of the soluble materials have been washed out, 
tending to leave high percentages of the persistent ma- 
terials, such as silica, iron, and aluminium. An analysis 
of an Arkansas limestone, its residual clay and the cal- 
culated percentage loss of the various constituents pres- 
ent in the fresh rock, illustrates this point : — 



GEOLOGICAL CLASSIFICATION OF SOILS 33 

Arkansas Limestone and its Residual Clay i 



SiOj 

AI2O3 

FeaO, 

MnO 

CaO 

MgO 

K2O 

NajO 

CO2 



Fresh Rock 



4.13 

4.19 

2.35 

4.33 

44.79 

.30 

.35 

.16 

34.10 



Clay 



33.69 

30.30 

1.99 

14.98 

3.91 

.26 

.96 

.61 

.00 



Percentage 
Lost 



.00 
11.35 
89.56 
57.59 
98.93 
89.38 
66.36 
53.26 
100.00 



The vast age of such soils tends to bring about great 
oxidation, so that most of the iron has changed to hematite 
and Hmonite. Since almost all soils contain considerable 
iron, the prevailing colors of residual soils are reds and 
yellows, depending on the degree of oxidation and hydra- 
tion. Grays and browns may exist, however, where iron 
has been lacking or oxidation has been feeble. In texture 
such soils usually present very fine conditions. Having 
been attacked by both the physical and the chemical 
agencies, the particles have been reduced to a very fine 
state of division. Qv^er residual areas the heavier soils 
predominate, as silts, silt loams, clays, and clay loams. 
Very often sand or chert may be present, having been a 
constituent of the original rock mass. 

An examination of the particles of a residual soil usually 
shows them to be in an advanced stage of decay. The 
feldspars have lost their luster and have become opaque. 
The iron has become oxidized, and the soluble bases have 



^ Penrose, R. A. F. 
Vol. I, p. 179. 1890. 

D 



Ann. Rept. Geol. Survey Arkansas, 



34 SOILS: PROPERTIES AND MANAGEMENT 

either disappeared or changed their combinations to more 
stable forms. The tendency of all soils is toward a con- 
dition of equilibrium, and consequently they approach, 
but never reach, a common composition. This does not 
apply to their productivity, because many other factors 
besides chemical composition go to determine cropping 
power. Residual limestone soils, therefore, become^poorer 
and poorer in lime as their age increases. The organic 
matter of residual soils largely depends, in amount and 
condition, on climatic factors. If rainfall and tempera- 
ture, for instance, are favorable for the rapid and con- 
tinued development of a natural vegetation, the soil 
will be rich in humus, so rich at times as to mask to a 
certain extent the red color so characteristic of such soils. 
If plants do not grow Avell on this soil, however, it will be 
low in organic matter and probably in poor physical con- 
dition, so vital is humus to a proper foothold for plant 
life. Two residual soils coming from the same kind of 
rocks may vary rather widely in their general character- 
istics, especially as to crop productivity. 

26. Distribution of residual soils. — Residual soils are of 
wide distribution in the United States,^ particularly in the 
eastern and central parts. A glance at the soil map of this 
country (See Fig. 4) shows four great provinces — the Pied- 
mont Plateau, the Appalachian Mountains and Plateaus, 
the Limestone Valleys and Uplands, and the Great Plains 
Region, The age of these soils varies in the order named, 
showing that while they are very old as compared with 
other soils yet to be discussed, there may be vast periods 
of geologic time between their beginnings. As a matter 

• For a full discussion of the origin and characteristics of the 
soils of the United States, see Marbot, C. F., and others. U. S. 
D. A., Bur. Soils, Bui. 96. 1913. 




Fio. 4. — Map show-iiig the soil provinces and soil regions 



of the United States. Bureau Soils. Bui. 96, 1913. 



GEOLOGICAL CLASSIFICATION OF SOILS 35 

of fact, there is probably a greater difference in age be- 
tween the soils of the Piedmont Plateau and those of 
the Great Plains Region than has elapsed since the latter 
were formed. The soils of the Piedmont Plateau have 
been formed mostly from gneiss and schist. In fact, 
the Piedmont Plateau is the remnant of the old continent, 
Appalachia, which was in existence in early Cambrian 
times. The rocks of the Appalachian Mountains and 
Plateaus are limestone, sandstone, and shales. The Great 
Plains Region presents limestone, sandstone, and shale 
of the Cretaceous, Permian, and Carboniferous ages, be- 
sides much unconsolidated material. The soils of these 
provinces, extending as they do over great areas, vary 
within wide limits due to rock formation, climatic con- 
ditions, and age ; yet certain common characteristics, 
as already pointed out, are exliibited by all. 

27. Cumulose soils. — This type of soil is of a very 
different character from the one just under discussion, 
being made up largely of organic matter with the mineral 
constituents of secondary importance. At relatively 
recent periods shallow lakes, ponds, and basins were 
formed, partly by stream action, partly by marsh con- 
ditions along sea or lake coasts, or, what is commoner in 
the northern part of the United States, by glaciation. 
Any basin that contains water throughout the year serves 
as a place for the formation of cumulose soil. The highly ^ 
favorable moisture relations along the banks and shores 
of such standing water encourage the growth of many 
plants such as algse, moss, reeds, flags, grass, and the like. 
These plants thrive, die, and fall down only to be covered 
by the water in which they were growing. The water 
shuts out the air to a large extent, prohibits rapid oxida- 
tion, and thus acts as a preservative for the rapidly collect- 



36 SOILS: PROPERTIES AND MANAGEMENT 

ing organic matter. Year after year this process goes 
on, and year after year the bed of cumulose material 
becomes deeper and deeper. Large shrubs, and even 
forests, often grow on such land. Time and the lack of 
water are the factors that may limit the depth of such 
beds. Accumulations of this nature are found dotted 
over the entire country. Their size may vary from a 
few acres to several thousand. Along streams the old 
abandoned beds offer a common opportunity for the 
beginning of such accumulations. Along large bodies 
of water, marshes, either salt or fresh, may allow the 
process to go on. Shallow basins scraped and gouged 
out by advancing glaciers are frequently occupied by 
such material. In the last-named case the beds are 
more or less independent of topography, and may be 
found on hillsides, or even on hilltops, as well as in the 
lower lands. 

Cumulose materials may be grouped under two heads, 
peat and muck. The only difference is in their stage of 
decay. In peat the stem and leaf structure of the original 
plants can still be detected, and identification is quite 
possible. In muck, however, the putrefaction and decay 
have gone so far that the plant tissue has lost its 
identity as such and is merged into that complicated 
and indefinite material called humus. The composition 
of peat and muck may be much altered by the wash- 
ing-in of mineral matter from above. In some cases 
the beds may be from 80 to 85 per cent organic, while 
in other cases, due to this foreign material, the percent- 
age may drop to as low as 15, giving a black or swamp 
marsh mud. 

The following analyses illustrate the composition of 
representative cumulose soils : — 



GEOLOGICAL CLASSIFICATION OF SOILS 



37 



Mineral matter 
Organic matter 
Nitrogen . . 
P2O5 .... 
K.,0 .... 
Moisture . . 



31.60 

68.40 

2.63 

.20 

.17 



24.79 

67.63 

2.03 

.19 

.15 

7.58 



80.40 
15.77 

.15 

.65 

3.83 



1. Muck — Piekel, G. M. Muck : Composition and Utili- 
zation. Fla. Exp. Sta., Bui. 13. 1891. 

2. Muck — Rept. Can. Exp. Farms, 1910. Rept. of chem- 
ist, p. 160. 

3. Marsh mud — Rept. Can. Exp. Farms, 1910. Rept. of 
chemist, p. 137. 

Muck soils, while usually not of large extent, become of 
extreme value when drained, especially if they are near 
a good market. They are of particular value in trucking 
operations, being adapted to such crops as onions, celery, 
lettuce, and the like. Usually they must not only be 
provided with drainage, but also be treated with fertili- 
zers carrying phosphorus and, especially, potash. It is 
also a good practice to start vigorous decay by the appli- 
cation of barnyard manure, as the nitrogen carried by 
muck soils is usually not very readily available to plants. 
In many cases muck and peat may be imderlaid at vary- 
nig depths by marl, which is a soft, impure calcium 
carbonate. Before and at the beginning of the organic 
accumulation these basins were inhabited by Mollusca, 
which at death deposited their shells on the bed of the 
inclosure. These shells are now found in a more or less 
fragmentary condition, usually mixed with sand and 
clay and covered to a varying depth with peat or muck. 
Such material, because of its richness in lime, is valuable 



38 



SOILS: PROPERTIES AND MANAGEMENT 



as a soil amendment, and often where it is found pure 
enough in quahty and in sufficiently large quantities it 
is handled commercially. When it contains large amounts 
of phosphorus, as it does in some cases, it may be used 
as a fertilizer. The following analyses ^ show the general 
character of this soil : — 



SiOa . . 
AI2O3 . FeaOs 

CaO . . 

MgO . . 

K2O . . 

NasO . . 

P2O5 . . 

CO2 . . 
Ignition 



25.28 


5.65 


3.02 


3.30 


37.52 


48.51 


.12 


1.96 


.22 


.23 


.25 


.30 


.40 


Trace 


29.02 


39.80 


4.17 


.25 



28. Colluvial soils. — This class of soil is not of great 
importance, first because of its small area and its inac- 
cessibility, and secondly because it is usually a coarse, 
loose soil, rather unfavorable for plant growth. It is 
formed, as its name indicates, in regions of precipitous 
topography,, and is made up of fragments of rocks de- 
tached from the heights above and carried down the 
slopes by gravity. Talus slopes, cliff debris, and other 
heterogeneous rock detritus are examples of colluvial 
soil. Avalanches are made up largely of such material. 
As the physical forces of weathering are most acti\'e in 
the formation of these soils, the amount of solution and 
oxidation is small. The upper part of the accumulation 



1 Kerr, W. C. 
1875. 



Geology of North Carolina, Vol. I, p. 195. 



GEOLOGICAL CLASSIFICATION OF SOILS 



39 



exhibits this isolated physical action to the greatest extent, 
the particles being angular, coarse, and comparatively 
fresh ; farther down the slope the material may merge 
by degrees into ordinary soil. Such soils are usually 
shallow and stony, and approach the original rock in 
color unless large amounts of organic matter have ac- 
cumulated (Fig. 5). 




Fig. 5. — Diagram showing the formation of a colluvial soil, (a), bed 
rock ; (6), dismantled cliff ; (d), coarse unproductive talus ; (p), soil 
capable of bearing plants. 



29. Alluvial soils. — In considering the importance of 
water as a weathering agent, it was found that it had 
both cutting and transporting powers. The alluvial 



40 SOILS: PROPERTIES AND MANAGEMENT 

soil is a direct result of both these activities. The earn- 
ing power of water varies directly as the sixth power of 
its velocity ; so that a doubling of the velocity increases 
the transportive ability sixty-four times. It is estimated ^ 
that water flowing at the rate of three inches a second 
will carry onl}' fine clay, but if this rate is increased to 
twenty-four inches a second, pebbles the size of an egg 
will be moved along the stream bed. Any checking of 
the velocity of a stream will cause it to deposit the ma- 
terial carried in suspension, the larger particles first and 
the finest when the current becomes very sluggish. This 
brings about one of the important characteristics of an 
alluvial soil, its stratification. Wherever material is 
being laid down by water this phenomenon is exhibited, 
due to the rapid changes in velocity. As a stream ap- 
proaches nearer and nearer to its outlet, its bed becomes 
less and less inclined and the current more and more 
sluggish. This tends toward an aggrading of the stream 
bottom from the deposited material. Such a condition 
naturally increases the probability of overflow in high 
water. Overflow at a time when the stream is carrying 
its maximum of sediment causes the deposition of a thin 
layer of soil over the areas covered by the water. This 
soil is stratified according to the conditions under which 
it was laid dowTi, the finer particles usually being carried 
farther and often deposited in slack water or lagoons. 
Also, a stream on a gently inclined bed may begin to 
swing from side to side in long, gentle curves, due to the 
deposition of alluvial material on the inside of the curve 
and the cutting by the current on the opposite bank. 
This results in oxbows, lagoons, and similar inclosures, 

1 Geikie, A. Text Book of Geology, p. 380. New York. 1893. 



GEOLOGICAL CLASSIFICATION OF SOILS 41 

ideal for the deposition of alluvial matter. Deltas are 
another good example of alluvial deposits, whether oc- 
curring in ocean, gulf, or lake. Due to a change in grade, 
a stream may cut down through its already well-formed 
alluvial deposit, leaving terraces on one or both sides. 
Often two, or even three, terraces may be detected along a 
valley, marking a time when the stream bed was at 
these elevations. On the lower slopes of hills border- 
ing valleys, the colluvial deposits may touch or even 
mingle with the alluvial, and furnish a stream with some 
of its detritus. 

Alluvial soils, then, are found as narrow ribbons along 
streams. They are always young soils, and are still in 
process of formation. Since m most cases they are de- 
posited by slowly moving water, the texture of such soils 
is fine, the soils being mostly clays, silts, and fine sandy 
loams. Found in low lands, alluvial soils need drainage 
to a large extent. Because of the favorable moisture con- 
ditions these soils usually have a very large amount of 
organic material, as vegetation grows readily under such 
conditions. Considerable humus is also washed into 
alluvial materials at the time of their deposition. The 
soil is usually deep, and, because of the high organic con- 
tent, universally of good physical condition, although 
very heavy stiff clays may be found in certain cases. 
The character of the soils and the rocks from which the 
detritus has been obtained exerts considerable influence 
on its character. For example, a red soil will often 
give rise to a reddish alluvial soil, while a soil or a rock 
poor in lime will certainly not be parent to a soil very 
much richer in that constituent. 

30. Distribution of alluvial soils. — The distribution 
of alluvial soils in the United States is not wide, although 



42 



SOILS: PROPERTIES AND MANAGEMENT 



these soils exist along almost every stream east of the 
Great Plains Region. Their best and widest develop- 
ment is found, as the map indicates (See Fig. 4) along 
the lower Mississippi river, where they may often show 
a lateral extension of one hundred miles. Extensions of 
this band are noted along the jNIissouri, Ohio, and I'pper 
Mississippi rivers. All streams flowing east exhibit 
areas of such soils, these areas varying with the size and 
velocity of the stream. 

The soils of the alluvial province may be divided under 
two heads because of topographic differences — (1) the 
first bottoms, or present flood plains ; and (2) the terraces, 
or old flood plains. These soils differ in their elevation, 
drainage, and age, but their general characteristics are 
similar ; the surface features in both cases vary from a flat 
to a gently rolling topography (Fig. 6). Erosion, especially 
in the terraces, may have obliterated some of the out- 




FiG. 6. — Cross-section of typical alluvial soils. (o), bed rock; 
(r), stream; (6), present flood plain, a recent alluvial soil ; (c), flood 
plain terrace; (d), very old stream terrace, an old alluvial soil. 



standing features. Alluvial soils, being very rich, are 
particularly adapted to trucking crops, although in most 
cases they are utilized for more extensive farming. When 
well drained and protected from overflow, they are the 
richest and most valuable of soils. 



GEOLOGICAL CLASSIFICATION OF SOILS 43 

31. Marine soils. — The sediments which are con- 
tinually being carried away by rivers are eventually 
deposited in the sea, the coarser fragments near the 
shore, the finer particles at considerable distances. This 
layer of material, varying in thickness, consists of stratified 
gravels, sands, and clays, and is of a rather recent age 
compared with the residual soils. It has not become 
consolidated as yet, because of insufficient pressure and 
time. When such material becomes raised above the 
sea, due to a change in land elevation, it is classified as a 
marine soil. It has been worn and triturated by a num- 
ber of agencies. First, the forces necessary to throw it 
into stream suspension were active, and next it was 
swept into the ocean to be deposited and stratified, 
possibh- after being pounded and eroded by the waves 
for years. At last came the emergence above the sea 
and the action of the forces of weathering in situ. The 
latter effects are not of great moment, since with our 
most important marine soils they have been at work 
for but a comparatively short time, speakmg geologically. 

32. Characteristics of maa-ine soils. — Marine soils, 
while much younger than residual soils, are usually more 
worn and ordinarily show a less amount of the important 
food elements. This is because of their almost con- 
tinuous contact with water from the time when they are 
swept into the streams until they rise above the sea level 
as a soil. They are generally characterized as sandy 
soils, because the forces to which they have been sub- 
jected have worn out and dissolved most of the minerals 
except quartz. This gives them a coarse texture and 
fits them particularly for trucking soils. Sands, sandy 
loams, and loams predominate usually in such soil prov- 
inces, although clays and silts may occasionally be 



44 SOILS: PROPERTIES AND MANAGEMENT 

found. These soils are usually low in humus, and con- 
sequently must be handled with reference to the possi- 
bilities of increasing their organic content. Lack of 
humus makes the predominating color of the soil light, 
ranging from light gray to brown and dark brown. The 
character of these soils is governed to some extent by the 
origin of the sediments ; different rocks, particularly if 
weathered under different climatic conditions, may give 
rise to widely different marine soils. The climatic con- 
ditions to which marine materials are subjected after 
being raised above the sea may also be a considerable 
diversifying agency. 

33. Distribution of marine soils. — INIarine soils are 
found very widely distributed in the eastern United States, 
and make up one of our most important soil provinces. 
Beginning at Long Island at the north (See Fig. 4), 
they extend southward along the coast in a band ranging 
from one hundred to two hundred miles in width. The 
western edge of the Atlantic coastal plain is marked by 
the great " Fall " Line, or the edge of the old continent 
Appalachia. It is from this area that most of the sedi- 
ments of the Atlantic marine soils were derived. Proceed- 
ing southward, we find that Florida is practically all of 
marine origin, together with a great area of the Gulf 
coast extending westward to central Texas and having 
an average width of two hundred fifty miles. This 
gulf marine soil is considerably younger than that of 
the Atlantic coast. It is cut into two parts by the allu- 
vial soils of the Mississippi, and is covered by a narrow 
band of alluvial soil on the eastern bank of that stream. 
The sediments of the Gulf coastal plain were derived 
from the erosion and denudation of the old lands to the 
northward. 



GEOLOGICAL CLASSIFICATION OF SOILS 45 

The soils of the Atlantic and Gulf coastal provinces, 
formed as ^'ast outwash plains, are very diversified, due 
to source of material, age, and climatic conditions. They 
comprise a sufficient range in texture and climate to 
support a highly varied agriculture. There are great 
tracts of general farming land, besides wide areas of 
special-purpose soils adapted to highly specialized in- 
dustries. The latter soils require refined and intensive 
methods of cultivation. Predominantly sandy, these 
soils are easy to cultivate, and they are well drained 
except in the lower coastal plain belt. Good aeration is 
usually found because of their open structural condition. 
Severe leaching occurs in times of heavy rainfall, for the 
same reason. When sufficiently supplied with organic 
matter, carefully fertilized, and cultivated properly, 
these soils support a great variety of crops, such as cotton, 
corn, oats, forage crops, and peanuts, besides vegetables 
and fruits of many varieties. 



CHAPTER IV 

GEOLOGICAL CLASSIFICATION OF SOILS 
(CONTINUED) 

Ice in the form of glaciers has been, as already stated, 
a very great factor in soil formation, especially in the 
north temperate zones of North America, Europe, and 
Asia. Not only was the old mantle of material swept 
from the land by the advance of the ice, but a new soil 
was laid down as drift material. This drift was some- 
times merely ground-up rock, sometimes rock flour 
mixed with the original residual soil, and sometimes 
glacial material wholly reworked and considerably strati- 
fied by water. Besides this, the streams of water that 
issued from under the glaciers were instrumental in 
many cases in distributing sediments a considerable 
number of miles southward of the ice front. Glacial 
lakes, also, when in existence for sufficiently long periods, 
furnished basins for the distribution and deposition of 
materials derived from the erosive and grinding power 
of the ice. The ice also furnished a large amount of 
very fine detritus, which was susceptible to wind move- 
ment. This material, reworked and deposited as bars 
in stream beds, was carried many miles by the prevailing 
westerly winds duruig a period of aridity following the 
glacial epoch. It now exists over wide areas, especially 
in the INIiddlc West of the United States and in northern 
China, in which places it reaches its best development. 

46 



GEOLOGICAL CLASSIFICATION OF SOILS 47 

It is the important soil of these regions. Glaciation was 
instrumental, then, either directly or indirectly, in the 
formation of three general classes of materials — glacial 
drift soils, glacial lake soils, and a certain class of ^Eolian 
materials designated as loess and adobe. 

34. The ice sheet.^ — If in any region, but more likely 
one of some elevation, the temperature and the snowfall 
stand in such relationship that the heat of summer does 
not offset the winter accumulation of snow, great snow 
fields form. As this condition persists year after year, 
and the snow becomes deeper and more widely spread, 
the temperature is reduced to such an extent as to in- 
crease the proportion of the precipitation which persists 
through the summer's heat. The pressure of the over- 
lying snow, and the water from the melting surface, bring 
about a change of the snow into ice. Often a recrystalli- 
zation appears to occur without a melting and refreezing. 
As the depth of ice increases, the phenomenon of move- 
ment is inaugurated as the thickness of the ice at the 
center develops strong lateral pressure. Ice, when under 
great stress, exhibits a plasticity which it does not or- 
dinarily possess. As it moves slowly forward under 
this tremendous pressure, and with a thickness of develop- 
ment almost incredible, it conforms itself to every un- 
evenness of the surface it may be invading. It rises over 
hills, or shapes itself to valleys and even small depressions, 
with surprising ease. The rate of advance or retreat of 
a glacier is determined by the rate at which its edges 
are wasting or melting away. If the melting is slow, the 
ice front advances ; if it just balances the advance, the 

' For a complete discussion of glaciers and glaciation, see 
Salisbury, R. D. The Glacial Geology of New Jersey. Geol. 
Survey of New Jersey, Vol. 5. 1902. 



48 



SOILS: PROPERTIES AND MANAGEMENT 



ice front is at a standstill ; })ut if the wasting is ra})i(l, 
and the advance of the glacier is not fast enough to re- 
place this waste, the ice is said to be retreating. A great 
ice sheet may exhibit all three of these conditions many 
times in its history. 




Fig. 7. — Map of North America, showing the area covered by the 
great ice sheets, the three centers of accumulation, and the approxi- 
mate southward extension. 



35. The American ice sheet. — The northern part of 
the American continent was at one time covered by a 



GEOLOGICAL CLASSIFICATION OF SOILS 49 

great sheet of ice possessing all the properties described 
above. Accumulation seems to have occurred in three 
well-defined centers, from which, over long geologic 
periods, the ice slowly moved southward, encroaching 
upon and covering thousands of square miles. The 
ice cap of Greenland is a very good example of the con- 
ditions then existing in the northern part of the United 
States. The area covered by glaciers in North America 
at the time of the greatest extension of the ice is estimated 
as 4,000,000 square miles. The thickness of the sheet 
was probably very great, ranging from a few feet at the 
margin to probably a mile or more toward the centers; 
at least it was thick enough to override some of the 
highest mountains of the New England ranges. Local 
glaciation also occurred on the hill and mountain tops, 
which tended to increase the apparent thickness of the 
ice mantle. 

36. Cause of the ice age. — The ice age was not one 
unbroken invasion and retreat of the ice cap, but was, 
as is conceded by all authorities on glaciation, really 
divided into epochs. Five great invasions appear to 
affect at least the central part of the United States, 
possibly without bringing about a disappearance of the 
ice across the Canadian border. These interglacial 
periods are shown by forest beds, accumulations of 
organic matter, and evidences of erosion between the 
drift deposited by the successive ice sheets. Some of 
the interglacial periods evidently were times of warm, 
and even semitropical, climate. Just exactly what was 
the cause of the ice age is still under dispute. The most 
probal)le theory, both as to its occurrence and as to its 
disappearance, is that a change in the carbon dioxide 
content of the atmosphere took place. It is believed 



50 SOILS: PROPERTIES AND MANAGEMENT 

that doubling the amount now present would bring about 
tropical climate in the temperate zones, while halving 
it would cause frigid conditions and a probable return 
of the great ice fields. 

37. The extension of the ice sheet. — While the 
advancing ice in general exliibited well-defined viscosity, 
certain parts were more or less rigid. This was especially 
true of the parts near the edges of the sheet. These 
parts had become filled in their advance, particularly 
near the bottom, with earthj^ and stony material, which 
aided the erosive processes to a very great degree. The 
eroding and denuding power of the glaciers is shown 
everywhere by the gouged-out valleys and by the scratches, 
or striae, on exposed rocks. As this sheet of ice slowly 
advanced a few inches or a few feet a day, the mantle of 
residual soil was carried away or mixed with the rock flour 
constantly formed by the moving ice. The original soil 
was really an instrument for more effective ice action. 
The scouring effect is observed now to the best advantage 
in valleys which lay longitudinally to the ice movement, 
as did the valleys of the Finger Lakes of central New 
York. Valleys lying at right angles to the ice were very 
often partially or wholly filled with debris, and the en- 
tire topography was altered. Rivers flowing under the 
ice often left large amounts of materials designated now 
as eskers and kamcs. The mixing, grinding, trans- 
porting, and stratification that went on emphasizes 
again the great influence of glaciation on general topog- 
raphy and soils. 

The greatest southward extension of the ice in the United 
States is marked by a great terminal moraine (Fig. 8). 
It is supposed that the margin of the sheet was stationary 
at this point for a sufficiently long period to allow this 



GEOLOGICAL CLASSIFICATION OF SOILS 



51 




52 SOILS: PROPERTIES AND MANAGEMENT 

narrow band of material to collect by the continual 
melting of the ice and a consequent dumping of its load 
of debris. This moraine is by no means continuous, 
and for miles across the continent no trace of it can be 
found. It extends, roughly, eastward from the Canadian 
border in Washington to the upper sources of the jNIissouri 
River, then down that river to St. Louis, up the Ohio 
River, northeastward until the southwest border of 
New York is reached, and then southeast to New York 
City and Long Island. Many other moraines are found 
to the northward, marking points where the ice became 
stationary for a time during its retreat. 

38. The ice as a soil builder. — It was during these 
retreats that the ice acted as a soil-forming agent. Ma- 
terial gathered and ground by the ice as it pushed to the 
southward was finely pulverized and it is only natural 
to suppose that this debris was deposited as the ice slowly 
retreated by the melting back of its margins. The 
material laid down as a great mantle over the glaciated 
areas is called drift. Some of this has been reworked 
and stratified by water, but a very large proportion has 
remained untouched since it was laid down by the melt- 
ing ice. It presents in most cases — except at the very 
surface, where weathering may have occurred or organic 
matter accumulated — exactly the same condition as 
when deposited. This mass of unstratified material is 
heterogeneous, both as to size of the particles that make 
it up and as to its rock composition. It may be coarse 
and bowldery, especially in mountains or where there 
are gneisses or schists, or it may be very fine where the 
rocks are soft. Bowlder clay is a term sometimes used 
in describing the matrix of this glacial deposit. In some 
cases foliation occurs, and often coarse and fine layers 



GEOLOGICAL CLASSIFICATION OF SOILS 53 

of till may alternate. This great mantle of material, 
varying in thickness and constitution according to the 
underlying rocks and the strength of glaciation, gives a 
great soil province in northern United States which 
may be designated as glacial till soil. 

39. Glacial till soils. — The glacial till soils may be 
characterized physically as heavy or relatively heavy 
soils. The tremendous force of the grinding has pro- 
duced fine particles, and as a consequence clay loams 
and silt loams predominate. Such soils usually have a 
subsoil which is finer than the surface material and may 
be so impervious to water as to produce bad drainage 
conditions. The individual particles of a glacial soil 
are found to be un weathered to a great degree unless the 
soil is mixed with some of the old mantle of residual 
material which once overspread all our glaciated areas. 
The particles are jagged and unrounded ; the feldspars 
retain all of their luster, and the iron stains so common 
in residual soils are almost absent. As the glacial soils 
are young soils, their colors are seldom made up of reds 
and yellows, but grays and browns prevail. Red may 
occur, however, where red sandstones have been glaciated 
or where red residual soil has become incorporated in 
the till. Where considerable organic matter has accu- 
mulated the soil is usually very black. The subsoils 
in the glaciated areas usually present colors ranging 
from light grays to light browns. Blue or mottled clay 
or clay loam is often found, due to a lack of aeration in 
the soil ; to the soil expert such a condition near the sur- 
face indicates a need of drainage. 

40. Composition of glacial soils. — The chemical com- 
position of glacial soil approaches more nearly than that 
of any other soil the composition of the original rock. 



54 SOILS: PROPERTIES AND MANAGEMENT 

This close resemblance to the parent rock is not sur- 
prising, since glacial soil is ground-up rock material of 
recent formation on which the weathering agencies have 
as yet had little time for action. Therefore the amounts 
of the important constituents in such soil are governed 
largely by the composition of the original rock. The 
lime content is due to such a relationship, and the agri- 
cultural value of the soil is greatly influenced thereby, 
since large amounts of calcium are of great importance 
to soil fertility. The hill soils of central New York 
(Volusia series) come from shales poor in lime, and the 
soil owes its properties very largely to this lack, which 
is traceable to the parent rock. On the other hand, cer- 
tain glacial soils of the Mississippi Valley (]\Iiami series) 
formed from sandstones and limestone, contain plenty 
of lime due to the nature of their rock origin. Glacial 
soils from limestone always contain plenty of lime, a 
condition that is far from true with residual soils. 

41. Humus of glacial soils. — The humus content of 
glacial soils depends to a large extent on the climatic 
conditions under which the soil has existed since its 
formation. If environmental factors have been such 
as to encourage the accumulation of organic matter, 
these soils will exhibit the deep black color that arises 
from the presence of such material. If, however, con- 
ditions do not encourage the natural growth of a heavy 
vegetation, the amount of organic matter in such virgin 
soil will be low. Lime may be a very great factor in 
such soils, not only in the encouragement of plant growth, 
but also in the proper decay of the plant tissue after 
it has become incorporated with the soil. 

Glacial till soils are found distributed over all the area 
north of the great terminal moraine, and stretch, roughly, 



GEOLOGICAL CLASSIFICATION OF SOILS 55 

from New England to the Pacific coast (see Fig. 4). 
They comprise a great variety of soils, not only as to their 
physical character, but also as to fertility. They are 
adapted to many crops, but general farming is practiced 
on them to the greatest degree. This means extensive, 
rather than intensive, operations. In some localities 
dairying has been developed to a large extent, and has 
proved to be not only a means of obtaining paying re- 
turns from such soils, but at the same time a method of 
keeping up their fertility. 

42. Glacial lakes. — Such great masses of ice could 
not advance and retreat, again and again, on such an 
extensive scale, without causing the formation of great 
torrents of water. It is more than probable that at all 
times great streams gushed from the ice front, laden 
with much sediment. Often these streams were under 
pressure, which when released caused an immediate 
deposition of material. As long as the ice front stood 
south of the east and west divide, this water found ready 
egress and flowed rapidly away to deposit its load as 
gravelly outwash, river terraces, valley trains, and allu- 
vial fans. These formed alluvial soils of varied character, 
depending on the size of the materials carried. There 
came a time, however, in the retreat of the ice, when the 
front stood north of the divide and only a small pro- 
portion of the water found itself free to flow over the divide 
and away to the southward. The remaining water was 
ponded between the ice front and the old divide. Thus 
glacial lakes were produced, of large or small extent, 
according to the position of the ice. The location of 
such lakes is shown on the soil map of the United States. 
The ponded water remained in this condition for many 
years, subject, of course, to changes concordant with 



5fi SOILS: PROPERTIES AND MANAGEMENT 

the oscillation of the ice front. With the ice melting 
rapidly on the hilltops, these lakes were constanth' fed 
by torrents from above which were laden with sediment 
derived not only from under the ice, but also from the 
unconsolidated till sheet over which it flowed. As a 
consequence, there were in the glacial lakes deposits rang- 
ing from coarse delta materials near the shore to fine silts 
and clay in the deeper and stiller water. Such materials 
now cover large areas (see Fig. 4), not only in New York 
State and along the Great Lakes, but also in the Red 
River Valley and in the northerly inclined valleys of the 
Rocky Mountains and the Cascade and Sierra Xevadas. 
They make up by far the most important lacustrine 
soils. 

43. Lacustrine soils — glacial lake. — Glacial lake soils 
probably present as wide a variation in physical char- 
acteristics as any of our great soil provinces. Being 
deposited by water, they have been subject to much 
sorting and stratification, and range from coarse gravels 
on the one hand to fine clays on the other. They are 
generally found as the lowland soils in any region, al- 
though they may occur well up on the hillsides if the 
shores of the old lakes encroached thus far. The color 
of such soils varies from gray to black, according to 
the degree of organic matter present. The humus con- 
tent of such soils, as with the glacial till, varies with 
climate, and may be high, low, or medium according 
to conditions. The thickness of glacial lake deposits is 
variable, ranging from a few feet to many feet. In 
chemical composition they closely approximate the soil 
from which they are derived. This is particularly true 
as regards the presence of lime. The Dunkirk soil 
of southern Xew York, a wash from the lime-poor 



GEOLOGICAL CLASSIFICATION OF SOILS 57 

Volusia series of the highlands, is low in lime ; while 
the same soil just south of Lake Ontario, obtaining its 
wash from a limestone till (Ontario series), is rich in 
lime. As may be inferred from the above comparison, 
the glacial lake soils of the United States are variable 
in their fertility. 

The distribution of the glacial lake deposits, as seen 
from the soil map of the United States, is fairly wide. 
Such soils are found in areas large enough to be of great 
agricultural influence, extending from New England 
westward along the Great Lakes until their greatest 
expanse is reached in the Red River Valley. These de- 
posits make up some of the most important soils of the 
northern states. They are valuable not only for ex- 
tensive cropping with grain and hay, but also for fruit 
and trucking crops. The Ice Age was certainly not 
in vain as far as the production of fertile soils is con- 
cerned. 

44. Lacustrine soils — recent lake. — There is yet 
another lacustrine soil to be considered besides the one 
just discussed — recent lake soil. While the glacial lake 
deposits were formed many thousands of years ago, the 
lake soils of the second group are in process of construc- 
tion. It is a well-known fact in physical geography 
that lakes are only enlarged stream beds, and are doomed 
ultimately to be filled by river sediments. Such soils 
have been reclaimed to a certain extent, but their acreage 
is not large enough to give them the importance of 
the glacial lake soils. The lake soil is usually of a fine 
character, rich in humus, of good tilth. If properly 
drained, it is almost invariably highly productive, and 
is adapted to a variety of crops depending on climatic 
conditions. 



58 SOILS: PROPERTIES AND MANAGEMENT 

45. iflEolian soils. — During glaciation much fine ma- 
terial was carried miles below the front of the glaciers 
by streams that found their sources therein. This fine 
sediment was deposited over wide areas by the over- 
loaded rivers. The accumulations occurred below the 
ice front at all points, but seem to have reached their 
greatest development in what is now the IMissouri Valley. 
There, too, the sediment seemed finest, and, coming 
mainly from glaciated limestones, was very rich in cal- 
cium. It is generally agreed by glacialists that a period 
of aridity, at least as far as this particular region is con- 
cerned, immediately followed the retreat of the ice. 
The low rainfall of this period was accompanied by 
strong westerly winds. These winds, active perhaps 
through centuries, were instrumental in the picking-up 
and distributing of this fine material over wide areas 
of the IMississippi, Ohio, and Missouri valleys. One 
strong argument for this ^Eolian origin is that the soU is 
found in its deepest and most characteristic development 
along the eastern banks of the large streams. Especially 
noticeable is the extension down the eastern side of the 
Mississippi River almost to the Gulf of INIexico. This 
wind-blown material, called loess, is found over wide 
areas in the United States, in most cases covering the 
original till mantle. It covers eastern Nebraska and 
Kansas, southern and central Iowa and Illinois, northern 
Missouri, and parts of Ohio and Indiana, besides a wide 
band, as already noted, extending southward along the 
eastern border of the Mississippi River. Due to its 
mode of origin, its depth is always greatest near the 
streams and gradually becomes less farther inland. In 
places, notably along the Missouri and Mississii)pi rivers, 
its accumulation has given rise to great blutt's which 



GEOLOGICAL CLASSIFICATION OF SOILS 59 

bestow a characteristic topography to that region. The 
loess soil is found also covering the great areas of China 
and Siberia, and thus it is one of the important soils of 
the world. Another soil, made up, at least partially, of 
wind-blown material and found in Arizona and New 
Mexico, is called adobe. Volcanic soils of the western 
United States and elsewhere are to some extent of wind 
origin. Sand dunes are of iEolian origin, but these sink 
into insignificance as to agricultural value when com- 
pared with the soils named above, especially loess. 

46. Loess soils. — Loess is usually a fine calcareous 
silt or clay, of a yellowish or yellowish buff color. While 
it may be readily pulverized when subjected to cultiva- 
tion, it possesses remarkable tenacity in resisting ordinary 
weathering. The vertical walls and escarpments formed 
by this soil show one of its striking physical character- 
istics. In China ^ caves that house thousands of persons 
are dug in the defiles and canons existing in this deposit. 
Another feature of loess is the presence of minute vertical 
canals lined with a deposit of calcium carbonate. These 
canals are supposed to give the soil its vertical cleavage 
and its tenacity. The particles of loess are usually un- 
weathered and angular. Quartz seems to predominate, 
but large quantities of feldspar, mica, hornblende, augite, 
calcite, and other substances are found. 

A few typical analyses " are given below : 

1 Riehthofen, F. Chinese Loess. Geol. Mag., May, 1882, 
p. 293. 

2 Clark, F. W. The Data of Geochemistry. U. S. Geol. Sur- 
vey, Bui. 491, p. 486. 1911. 

A. From near Dubuque, Iowa. 

B. From Vicksburg, Mississippi. 

C. From Kansas City, Missouri. 

D. From Cheyenne, Wyoming. 



60 



SOILS: PROPERTIES AND MANAGEMENT 





A 


B 


c 


D 


SiOa 


72.68 


60.69 


74.46 


67.10 


A1203 












12.03 


7.95 


12.26 


10.26 


Fe.Oa 












3.53 


2.61 


3.25 


2.52 


MgO 












1.11 


4.56 


1.12 


1.24 


CaO . 












1.59 


8.96 


1.69 


5.88 


NaaO 












1.68 


1.17 


1.43 


1.42 


K2O . 












2.13 


1.08 


1.83 


2.68 


P2O5 . 












.23 


.13 


.09 


.11 


CO2 . 












.39 


9.64 


.49 


3.67 


H2O . 












2.50 


1.14 


2.70 


5.09 



It is immediately noticeable that the lime coiitent of 
these soils is high, as is also the phosphoric acid. In 
fact, all the more soluble constituents are present in 
relatively large quantities, as would naturally be ex- 
pected from the mode of origin of such soils — they having 
been subjected to aridity and then deposited by the wind 
at a relatively recent period. It is maintained by some 
geologists ^ that the deposition of loess is still going on 
in certain parts of the world, but that the rate of accumu- 
lation is so exceedingly slow that it escapes the notice 
of all but trained observers. The lack of fossils, par- 
ticularly those of plants, is accounted for by this slow 
rate of formation, which allows sufficient time for all 
organic matter to become fully oxidized before being 
covered by the drifting material. Snail shells are often 
found, but as they are of land species they argue against 
a water origin of loess. 



^ Merzbacher, G. The Question of the Origin of Loess. Mitt. 
Justus Perthes' Geogr. Anst., 59, pp. 16-18, 69-74, and 120-130. 
1913. 



GEOLOGICAL CLASSIFICATION OF SOILS 61 

47. Distribution of loess. — Not only is loess found 
over thousands of square miles in the central part of the 
United States, but it occurs elsewhere in large areas. 
It is greatly developed in northern France and Belgium, 
and along the Rhine in Germany, where it is an important 
soil in all the valleys that are tributary to that river. 
Silesia, Poland, southern Russia, Bohemia, Hungary, 
and Roumania, all have deposits of this highly fertile 
material. In Europe it extends from sea level to eleva- 
tions of 5000 feet, showing its independence of water 
as a formative agent. In China it is found over a very 
large part of the valley of the Hoangho, a region prob- 
ably larger in area than France and Germany combined. 
The thickness of the deposit is variable, ranging from a 
few feet to several thousand feet in certain places. The 
depth is practically always sufficient for any form of 
agricultural operations. 

Wherever moisture relations are favorable loess is an 
exceedingly fertile soil, due to its rich stores of potash, 
phosphorus, and lime. Its organic content is usually 
medium to high, depending on conditions. In general 
it may be classified as the richest soil in the world, 
considering its wide extension and the great variety 
of climate and of crops to which it is subjected. In 
the United States it occurs in the Corn Belt region, 
and might be called the great corn soil of the Mississippi 
Valley. 

48. Adobe soils. — The term adobe is a name applied 
to a fine calcareous clay or silt formed in a manner some- 
what like that in which loess is formed. It is supposed 
that, while part of the deposit came from the waste of 
talus slopes as mountains were weathered under conditions 
of aridity, the remainder had an origin similar to that of 



62 



SOILS: PROPERTIES AND MANAGEMENT 



loess.^ Certain characteristics also seem to indicate that 
the valley adobe might have been deposited by water.^ 
It appears, therefore, that, while the physical characters 
of all adobe are somewhat similar, its mode of origin and 
chemical composition may be variable. Below are the 
analyses ^ to two typical adobe soils : — 



Si02 . . . 

AI0O3 . . . 

Fe203 . . . 

CaO . . . 

MgO . . . 

K2O . . . 

NasO . . . 

CO2 ... 

P2O5 . . . 
Organic matter 



66.69 


44.64 


14.16 


13.19 


4.38 


5.12 


2.49 


13.91 


1.28 


2.96 


1.21 


1.71 


.67 


.59 


.77 


8.55 


.29 


.94 


2.00 


3.43 



Like the loess, adobe is an exceedingly rich soil, but 
it occurs in an arid or a semiarid region. When irrigated, 
its fertility seems inexhaustible. It is found in Colorado, 
Utah, southern California, Arizona, New ]\Iexico, and 
Texas. It has an especially wide distribution in New 
]\Iexico. Like loess its elevation is variable, ranging 
from sea level in California and Arizona to GOOO feet 
along the eastern border of the Rocky Mountains. Its 
maximum thickness cannot be estimated, as it is very 

^ Russell, I. C. Subaerial Deposits of the Arid Regions 
of North America. Cleol. Mag., August, 1889, pp. 342-350. 

^ Hilgard, E. W. Relations of Soil to Climate. U. S. Weather 
Bur. Bui. 3. 1892. 

' Merrill, G. P. Rocks, Rock Weathering, and Soils, p. 321. 
New York. 1896. 



GEOLOGICAL CLASSIFICATION OF SOILS 63 

little eroded and is supposed to be still accumulating. 
Some valleys are known to be filled to a depth of 3000 
feet with this material. Its characteristics are its fine 
texture, its great depth, its wide distribution, and its 
great fertility when moisture conditions are suitable for 
crop growth. 

49. Sand dunes. — Sand dunes are the outgrowth 
of two conditions — a large quantity of sand and a 
wind that blows in a more or less prevailing direction. 
Under such conditions the sand and other fine material 
not only is blown into heaps, but also tends to move in 
the direction of the prevailing wind. Such heaps or 
mounds of sand may travel several feet a day by the 
continual movement of the sand grains up the windward 
side of the dune, only to be deposited again on the lee- 
ward side. Sand dunes may often assume gigantic 
proportions, being sometimes several hundred feet high 
and twenty or thirty miles long. In such proportions 
they become a gra\-e menace to agriculture, not only 
because they are an absolutely valueless medium for plant 
growth, but also because they cover fertile lands and 
entirely blot out all plant growth. The particles of this 
wind-blown sand are usually round, from the continual 
abrasion that they receive. A great many minerals 
may be represented, but quartz is the commonest, es- 
pecially if the dune originally had its origin on a lake or 
a seashore. 

50. Volcanic dust. — From early geologic times de- 
posits of the very fine material that is continually being 
ejected from volcanoes have been distributed o^'e^ the 
earth's surface. These deposits are usually flour-like, 
and while at one time they probably covered many 
square miles of territory, they have succumbed very 



64 SOILS: PROPERTIES AND MANAGEMf^NT 

largely to erosion and denudation, and only remnants 
are found at the present time. Such material may be 
found in IMontana, Nebraska, and Kansas. ^-lOolian 
deposits of this character are usually rather porous and 
light, and are likely to be highly siliceous. They are 
not of great agricultural importance. 



CHAPTER V 

CLIMATIC AND GEOCHEMICAL RELATION- 
SHIPS OF SOILS 

Although during the process of weathering the tendency 
of all soil is toward a common composition, such a con- 
dition is never reached, due to different khids and varying 
intensities of decay and disintegration. Soils lend them- 
selves readily to a geological classification because of this 
difference in mode of formation. Such a classification 
really signifies a variation in composition. A difference 
in age, a preponderance of physical agencies over chemi- 
cal or vice versa, a difference in the transportive agencies, 
or a variation in climatic conditions after a soil is once 
formed, will assuredly give a different product, not only 
chemically, but physically and biologically as well. 

51. Climatic relationships. — It is evident that climate 
is a factor in all geochemical relationships of soils. Not 
only does climate determine the kind of weathering and 
its intensity, but in many ways it influences very largely 
the characteristics of the soils of different provinces and 
sections. Climate must be considered also in the geo- 
logical classification of soils, since it plays such an im- 
portant role in determining the kind and intensity of the 
formative agents. In any scheme of grouping for the 
systematic survey and mapping of soils, climate is the 
very first factor to be considered. It gives three great 
groups — tropical, subtropical, and temperate. These 
may in turn be subdivided into arid, semiarid, and humid. 
F 65 



66 



SOILS: PROPERTIES AND MANAGEMENT 



In the utilization of soil, climate, particularly as regards 
rainfall and temperature, plays an important part. Crop 
adaptation is really more of an adaptation to climate than 
to soil, although the latter also should be very carefully 
studied. The climatic relationships in soil formation, 
in soil chemistry, and in geochemistry in general, cannot 
be too strongly emphasized, whether the viewpoint be 
technical, practical, or merely educational. 

52. Geochemical relationships of residual and marine 
soils. — It is evident from the above that coastal plain, 
residual, and glacial soils should exhibit certain well- 
defined general differences due to their mode of formation. 
The following analyses, which are representative of the 
provinces in question, illustrate the chemical differences 
of coastal plahi and residual soils : — 

Analyses of Typical Coastal Pl.a.in axd Residual Soils 





Light Sandy 
Loam prom 
Maryland 

Average of 
5 Samples ' 


Corn and 
Wheat Clay 

Loam Soil 
Average op 

3 Samples' 


Residual 

Soil from 

Virginia 

Gneiss 2 


Residual 

Soil from 

Virginia 

Limestone' 


SiOa 

Al.O,, 

Fe^O., .... 
P2O5 ..... 

CaO 

CO2 

MgO 

Na^O 

K2O 


92.30 
3.20 
.91 
.05 
.41 
.08 
.35 
.50 
.70 


80.55 

8.82 

2.67 

.42 

.47 

.05 

.29 

.49 

1.22 


45.31 

26.55 

12.18 

.47 

trace 

trace 

.40 

.22 

1.10 


57.57 

20.44 

7.93 

.10 

.51 

.38 

1.20 

.23 

4.91 



1 Veiteh, F. P. The Chemical Composition of Maryland 
Soils. Maryland Agr. Exp. Sta., Bui. 70, pp. 71 and 73. 1901. 

2 Merrill, G . P. Weathering of Micaceous Gneiss in Albemarle 
County, Virginia. Bui. Geol. Soe. Amer., Vol. 8, p. 160. 1879. 

* Diller, G. S. The Educational Series of Rock Specimens. 
U. S. Geol. Survey, Bui. 150, p. 385. 1898. 



CLIMATIC AND GEOCHEMICAL RELATIONSHIPS 67 

It is to be noted, in the first place, that siUca exists in 
large quantities in the coastal plain soils, due to the fact 
that quartz is such a resistant mineral. The constant 
washing that this soil has undergone has very largely 
decomposed the silicates. The aluminium and iron are 
rather low on the average in such soils, even in those of 
the richer type. It is to be noted also that the amounts 
of phosphoric acid, calcium, potash, magnesia, and sodium 
are much less in the marine soils, due to the excessive 
washing that they have received. These figures would 
lead to the belief that in general the marine soils are 
lower in the mineral plant-food constituents than soils 
formed in situ. The amount of organic matter that they 
may contain depends entirely on their location and 
climatic conditions. They may or may not be rich in 
humus, according to circumstances. It is generally con- 
sidered, however, that they are not so well supplied with 
the organic elements as are other soils. 

53. Residual and glacial soils. — A comparison of 
residual and glacial provinces cannot be made with such 
assurance, because of the many kinds of rocks that may 
have been parent to the soils and because of the great 
variety of climatic conditions under which the soil-form- 
ing processes may have gone on. Such a comparison is 
best made in a region where both residual and glacial soils 
are found, as nearly as it is possible to judge, coming 
from the same rocks. Analyses of soils under such con- 
ditions are available, from the driftless and glaciated 
parts of Wisconsin. The original rock was limestone. 
The analyses ^ are as follows : — 

^ Charaberlin, T. C, and Salisbury, R. D. The Drift- 
less Area of the Upper Mississippi. Sixth Ann. Rept., U. S. 
Geol. Survey, pp. 249-250. 1885. 



68 



SOILS: PROPERTIES AND MANAGEMENT 



Analyses of Residual and Glacial Clays from the Drift- 
less AND Glaciated Areas of Wisconsin 





Residual 


Glacial 




1 


2 


3 


4 


SiO: 

AI2O3 

FeaOs 

MgO 

CaO 

Na20 

K2O 

P2O5 

CO2 

H^O 


71.13 
12.50 

5.52 
.38 
.85 

2.19 

1.61 
.02 
.43 

4.63 


49.13 

20.08 

11.04 

1.92 

1.22 

1.33 

1.61 

.04 

.39 

11.72 


40.22 
8.47 
2.83 
7.80 

15.65 

.84 

2.36 

.05 

18.76 
1.95 


48.81 
7.54 
2.53 
7.95 

11.83 

.92 

2.60 

.13 

15.47 
2.02 



These analyses illustrate to very good advantage the 
beliefs entertained by Chamberlain and Salisbury regard- 
ing the differences between residual and glacial clays. 
Residual clay is designated by them as " rock rot," and 
glacial clay as " rock flour." The latter, being less 
weathered, retains a larger proportion of its easily soluble 
materials. It is to be noted here, as in the comparison 
of marine and residual soils, that silica, aluminium, and 
iron are lower in the soil subjected to the less amount of 
leaching, which in this case is the glacial clay. This in 
itself would serve to indicate that the important plant- 
food constituents are generally present in larger quanti- 
ties in the glacial clay. In fact, it would be expected 
that the glacial soils would approximate very closely the 
rock or rocks from which they came. The })h()s])horic 
acid, lime, sodium, magnesium, and potash of the residual 
soils in this case amount on the average to 5.73 per cent, 
while that of the glacial clays reaches the high figure of 
24.01 per cent. This is due largely to the great amount 



CLIMATIC AND GEOCHEMICAL liELATIONSHIPS 69 

of lime present, and again emphasizes the point that, 
while a glacial soil from a limestone is rich in lime, a 
residual soil from the same rock is usually poor in that 
constituent. Even loess, which has been subjected to 
some washing before being deposited, is a considerably 
richer soil than those of residual origin. 

It must be remembered, however, that these comparisons 
are of a general character and do not apply to all cases, 
since many glacial soils may be very much poorer in the 
plant-food constituents than some of the representative 
residual soils. Moreover, the physical condition of a 
soil is a great factor in productivity. As a matter of 
fact, the mere presence of plant-food is but one of a 
considerable number of factors that determine the crop- 
producing power of a soil. Also, the humus content of 
the soils of various provinces may be variable, due to 
climatic conditions. Neither are all glacial soils rich in 
lime, as that constituent is determined largely by the 
amount in the parent minerals. A rock poor in lime, 
therefore, must from necessity give rise, when glaciated, 
to a soil deficient in lime. This is well illustrated by the 
average analyses ^ of the loam soils of Ashtabula County, 
Ohio, originating from the glaciation of the lime-poor 
shales of that region : — 

CaO 25 

MgO 61 

P2O5 04 

K2O 1.87 

N .15 

Humus 1.70 

1 Ames, J. W., and Gaither, E. W. Soil Investigations. Ohio 
Agr. Exp. Sta., Bui. 261. 1913. 



70 



SOILS: PROPERTIES AND MANAGEMENT 



However, our major premise does seem to stand in a 
general way — that a glacial soil, other things being 
equal, contains a larger amount of the mineral plant-food 
constituents, and ordinarily a smaller amount of such 
materials as silica, iron, and aluminium, than does a 
corresponding soil of residual origin. 

The following data ' bring out the points already dealt 
with in their fullest significance : — 

Percentage of P2O5, CaO, MgO, and K2O in Soils of Dif- 
ferent Provinces 



Soils 


P2O5 


CaO 


MgO 


K2O 


Total 


7 Coastal plain . ... . 

3 Residual (crystalline) . 

10 Glacial 


.07 
.25 

92 


.14 

.67 
1.36 


.16 
.75 
.79 


.70 
2.08 
2.08 


1.07 
3.75 
4.45 









54. Effect of glaciation on agriculture. — These differ- 
ences between residual and glacial soils reflect on the 
general fertility of the soils. In a comparison of the 
driftless area of Wisconsin with the glaciated parts,- 
only 43 per cent of the former is improved as against 
61 per cent. of the latter, while the value of the farms 
on the glaciated soil averages 50 per cent higher. The 
same general differences appear between the glacial and 
residual soils of Indiana^ and Ohio.'' 



1 Failyer, G. H., and others. The Mineral Composition 
of Soil Particles. U. S. D. A., Bur. Soils, Bui. 54. 1908. 

- Whitbeck, R. H. The Glaciated and Driftless Portions of 
Wisconsin. Bui. Geog. Soe. Phil., Vol. IX, No. 3, pp. 10-20. 1911. 

^ Von Engeln, O. D. Effects of Continental Glaciation on 
Agriculture. Bui. Amer. Geog. Soc, Vol. XLVI, p. 246. 1914. 

^Ames, J. W., and Gaither, E. W. Soil Investigations. 
Ohio Agr. Exp. Sta., Bui. 261. 1913. 



CLIMATIC AND GEOCIIEMICAL RELATIONSHIPS 71 

Von Engeln/ in a comparison of glaciated soils with 
corresponding residual areas, was able to point out cer- 
tain general differences. The agricultural condition 
within the zone of glaciation was always consistently 
higher than that beyond the regions of drift accumulation. 
The extensive leveling due to glacial erosion and dep- 
osition had almost always resulted favorably for agri- 
cultural operations. Even the thickness of the drift 
was found to conserve the ground water supply. Not 
only did this author conclude that glacial soils were 
richer in soluble plant-food constituents than residual 
soils, but he also showed that glacial soils had a greater 
crop-producing power and a higher agricultural value. 
The dominant textural quality of glacial soils seems 
adapted to certain staple food crops, and, due to their 
intermingling, a considerable opportmiity for diversified 
and intensified farming is offered. It is therefore evident 
that in any study of soils, particularly those of the United 
States, a careful consideration of the effects of glaciation 
is necessary. The great ice sheet has been responsible 
in some cases for the rejuvenation of our soils, in others 
for the production of an entirely new soil mantle. Even 
the alterations in topography are factors not to be ignored., 

55. Arid and humid soils.^ — This distinction between 
soils due to differences in the formative process is always 
evident, but is particularly striking in a comparison of arid 
and humid regions. In areas of light rainfall the physical 
agents are dominant, and disintegration goes on very 
largely without decomposition. Under humid conditions, 

1 Von Engeln, O. D. Effects of Continental Glaciation on Agri- 
culture. Bui. Amer. Geog. Soc, Vol. XLVI, pp. 353-35.5. 1914. 

2 For a more complete discussion of this subject, see Hilgard, 
E. W. Soils, Chapters XX and XXI. New York. 1911. 



72 



SOILS: PROPERTIES AND MANAGEMENT 



however, the chemical forces are the determining factor 
as to the character of the soil. Arid soils are therefore 
usually coarser soils and their color is very likely to be 
light. Such soils are deep and uniform, there being 
but little difference between the surface and the subsoil. 
The soils of the humid regions are usually of fine texture, 
particularly in residual regions, since the chemical agencies 
have been so active. Various colors may develop because 
of oxidation, hydration, and the presence of organic matter. 
Such soils usually are not excessively deep, and are likely 
to be underlaid by subsoils heavier than the surface. 
The general physical condition and tilth of arid soil is 
uniformly better than that of regions of plentiful rainfall. 
Chemically, because of less leaching the arid soils con- 
tain more of the important mineral plant-food elements. 
The following analyses bring out the differences in a 
striking manner : — 



Arid Soils 
Average op 
573 Samples' 



Hdmid Soils 
Average of 
696 Samples' 



Average 
Composition of 

LiTHOSPHERE* 



Insoluble residue and soluble 

SiOa 

AI2O3 

FeoOs 

P2O5 

CaO 

MgO 

NasO 

K2O 

Water and ignition . . . 
Humus 



75.87 

7.21 

5.48 

.16 

1.43 

1.27 

.35 

.67 

5.15 

1.13 



88.21 

3.66 

3.88 

.12 

.13 

.29 

.14 

.21 

4.40 

1.22 



59.36 (SiO.) 
14.81 
6.34 
.29 
4.78 
3.74 
3.35 
2.98 



1 Hilgard, E. W. 
Weather Bur., Bui. 

2 Clarke, F. W. 
Survey, Bui. 491, p, 



The Relation of Soil to Climate. U. S. 
3. 1892. 

Data of Geochemistry. U. S. Geol. 
33. 1911. 



CLIMATIC AND GEOCHEMICAL RELATIONSHIPS 73 

It is immediately apparent that the arid soil is poorer 
in silica than the humid soil, but richer in iron and alumin- 
ium, indicating a less weathered condition of the feldspars. 
Due to a greater amount of leaching, the humid soil is 
much lower in phosphoric acid, lime, magnesium, sodium, 
and potassium. The humus in arid soils is somewhat 
lower than in the soils under better conditions of rainfall, 
as one would naturally expect. The amount of easily 
soluble material is higher in arid regions, due to the lack 
of heavy rain and the tendency for soluble salts to accumu- 
late. A comparison of the analyses above with Clarke's 
estimate regarding the composition of the earth shows 
that the humid-region soil has moved farther away from 
the average soil-forming rock than the soil produced 
under conditions of aridity. 

Biologically, organisms are found active at greater 
depths ^ in arid regions than in humid regions, because 
of the loose structure of arid soils and because of their 
good aeration. Such soils are seldom water-logged. In 
humid regions bacterial action is limited very largely 
to the surface foot of soil, since only there are the aeration 
and the food conditions adequate. The intensity of 
biological activity in arid soils is very largely governed 
by moisture, and when moisture conditions, are satisfied 
bacterial changes may be expected to take place rapidly. 
Cases are on record in which the soluble salts due to 
bacterial action have become of such concentration as 
to be toxic to plants. 

56. Soil color. — Another characteristic of soil is its 
color, which has originated during the processes of soil 

1 Lipman, C. B. The Distribution and Activities of Bacteria 
in Soils of the Arid Region. Univ. of Cahf., Pub. in Agr. Sei., 
Vol. I, No. 1,-pP- 1-20. 1912. 



74 



SOILS: PROPERTIES AND MANAGEMENT 



formation, largely through natural weathering agencies. 
This is really a phase of geochemistry, particularly as 
regards those tints that originate from the oxidation of 
the iron. Color has long occupied the attention of 
geologists and agriculturists, in the first place because 
it gives a clew to the mode of soil formation, and in the 
second place because it is to a certain extent an index to 
agricultural value. At the outset it must be understood 
that soil colors are not pure colors, although spoken of 
as such, but tints and shades. In soils it is possible to 
find almost any conceivable color, ranging from white 
sands to black swamp muds or the blood-red clays of the 
Piedmont region. The three coloring matters of soil 
may be classified as (1) the color arising from the mineral, 
(2) the color given by the humus present in the soil and 
around the particles, and (3) the reds or the yellows due 
to oxidization of the iron. These three primary, or 
basal, colors may be represented for convenience as 
follows : — 



WH/7E 



BLAC/( 




BfK)W/i/5H 



fifO 



Fig. 9. — A triangular representation of the tlircc primary soil colors 
and their mixtures. 



CLIMATIC AND GEOCHEMICAL RELATIONSHIPS 75 

A soil low in humus, and with the iron either absent or 
unoxidized, will be of a light color. Sea sands are good 
illustrations of this condition. A well-drained soil con- 
taining large quantities of organic matter will present a 
deep black color in spite of the oxidized iron, as the latter 
will be masked to a large extent. If humus is low or 
lacking and the iron is oxidized, a red or a yellow color 
may characterize the soil. As might be expected, there 
are blendings of these three primary colors, and grays, 
browns, and yellows of varying intensities are common. 

57. White and black soils. — The light colors in soils 
are not due to the agencies of weathering, but rather to 
a lack of such action. The cause of such coloration is 
therefore not hard to explain. The development of the 
black or dark colors and tints, being due to the accumula- 
tion of organic matter, indicates the operation of two 
favoring conditions : first, climatic agencies that stimu- 
late the luxuriant development of plants ; and, secondly, 
sufficient aeration to promote a favorable decay of such 
tissue. It is a well-recognized fact that in order to 
develop a black color from decaying vegetable matter, 
fairly good aeration must be provided. If such a con- 
dition does not prevail, the decayed material has a lighter 
hue and may exhibit toxic properties which will check 
or inhibit plant growth. The development of the black 
color, therefore, in a normal well-drained soil, is an in- 
dication of good soil sanitation. 

58. Red and yellow soils. — The presence of iron, as 
already noted, is a very important factor in rock weather- 
ing, and the discoloration due to its presence is an unfailing 
indication of chemical decay. The iron in minerals 
occurs usualh' as ferrous oxide, which is soluble, especially 
if the water circulathig among the rock fragments carries 



76 SOILS: PROPERTIES AND MANAGEMENT 

carbon dioxide. As this water comes in contact with the 
air, its excess of carbon dioxide is discharged and the 
oxides and carbonates of iron are deposited. Under 
this condition oxidation goes on rapidly, and the iron 
passes to the ferric state and becomes insohible. Thns 
it may be seen that iron imparts a fatal weakness to rocks 
and minerals in which it may exist, due to its solubility; 
yet from the oxidation that it undergoes, it tends to 
persist and accumulate in soils. A corollary might be 
added to the law of mineral resistance, to the effect that 
" the more iron a mineral contains, the more susceptible 
it is to the weathering agencies." 

Therefore, from the geochemical standpoint, the de- 
velopment of the red and yellow colors in soils has been 
the subject of considerable dispute from time to time. 
The red and yellow soils of the Cotton States frequently 
excite comment, especially as a difference in fertility is 
popularly recognized ; the red surface soil with a red 
subsoil being considered more fertile than a similar soil 
with a yellow subsoil. Crosby ' believes that the differ- 
ence in color is due to a difference in hydration of the 
iron oxides. The soil temperatures, particularly in 
tropical and su})tr()])i('al regions, have first tended to 
fully oxidize and hydrate the iron, and then to dehydrate 
the soil at the surface into the deep red color, leaving the 
subsoil yellow and causing the contrasts so markedly 
evident. The ultimate product of both oxidation and 
hydration would be limnite, a yellow mineral ; while 
if oidy oxidation were active, hematite, which imparts 
a red color, would result as a final product. A dehydra- 
tion of the limnite would cause the formation of hematite 

' Crosby, W. O. Colors of Soils. Proc. Boston Soc. Nat. Hist., 
Vol. 23, pp. 219-222. 1875. 



CLIMATIC AND GEOCHEMICAL RELATIONSHIPS 77 

or some intermediate product. The composition of the 
common iron oxides found in soils tends to support 
Crosby's explanation : — ■ 

Hematite .... Fe203 Red 

Turgite .... 2 FesOg . H2O 

Goethite .... Fe203 . H2O 

Limonite .... 2 F2O3 . 3 H2O 

Xanthosiderite . . FcaOg . 2 H2O 

Limnite .... Fe203 . 3 H2O Yellow 

^Merrill ^ holds the same idea, but thinks that the sur- 
face soil may contain relatively more iron than the sub- 
soil. He considers that the ferric iron oxides, because 
of their uisoluble nature, tend to accumulate at the 
surface, and because of their large quantities and because 
they are there subjected to more vigorous weathering 
action the vivid red colors tend to develop. 

The iron coloring matter usually exists as a coating ^ 
on the soil particles, although it may sometimes occur 
as concretions. It is found also that in general, but not 
always, the intensity of the color varies with the amount 
of iron present. From a large number of analyses com- 
piled by Robuison and ]\IcCaughey,^ the following figures 
may be obtained showing the authority for such a state- 
ment : — 

Average Iron Content of Percent of 

Soils Ferric Iron 

Deep reds to light reds 14.40 

Ochre yellow to yellow 8.85 

1 Merrill, G. P. Rocks, Rock Weathering, and Soils, p. 375. 
New York. 1906. 

^ Van Bemmelen, J. M. Beitrage ziir Kenntnis der Ver- 
untterungsprodukte dor Silicate in Ton-, Viilkanischen-, und Lat- 
erite-Boden. Zeit. Anorg. Chem., Bd. 42, Seite. 290-298. 1904. 

3 Robinson, W. O., and MeCaughey, W. J. The Color of 
Soils. U. S. D. A., Bur. Soils, Bui. 79, p. 21. 1911. 



78 SOILS: PROPERTIES AND MANAGEMENT 

This being true, the thicker the fihn, the greater is the 
intensity of the color. The same (luantity of iron, there- 
fore, would make a greater showing in a sandy soil than 
in clay, as the amount of internal surface of the former is 
comparati^■ely low and the film of iron oxide would there- 
fore be thicker. 

It is evident from the data already presented that 
the intensity of color arising from iron in the soil is due 
to several conditions. Without a doubt the oxidation 
that occurs is of primary importance, but the hydration 
that very often takes place is a powerful modifying agent. 
The thickness of the film, as determined by the amount 
of iron present or by the texture of the soil, is probably 
a factor having to do particularly with the intensity of 
the coloration, although the color or tint itself may be 
modified to a certain extent thereby. 

59. Agricultural significance of color. — The white or 
the black color of a soil indicates the lack or the presence 
of an important constituent, namely, organic matter. 
This matter not only tends to keep the soil in good 
physical condition, but also acts both as a plant-food 
and as a source of energy for bacteria and other soil 
organisms. A dark soil, provided its drainage and 
climatic conditions are favorable, is usually a rich soil. 
The dark color is no mean factor in temperature relation- 
ships, since not only does a dark soil absorb heat faster 
than a light soil, but the tendency of the former toward 
reflection and radiation is much restricted. This is 
important with crops which must go into the soil early 
in the season, or which need to be pushed rapidly to 
maturity. A dark color, with virgin soils especially, is 
an excellent guide to fertility and general agricultural 
value. 



CLIMATIC AND CEOCHEMICAL RELATIONSHIPS 79 

Red colors in soil often show low or medium organic 
content. Besides this, the presence of oxidized iron is 
always an indication of age. The residual soils of the 
Piedmont Plateau are especially characterized in this 
way. Age gives opportunities for leaching, and conse- 
quently a lack of the soluble bases may be expected in 
such soils. The reds and the yellows are characteristic 
of residual soils, or of soils that have arisen from them 
by erosion or glaciation. A red color is almost as efficient 
in the absorption of heat as is black ; so that the early- 
growth and quick-maturing tendencies of crops on a 
red soil, other things being equal, are about the same as 
on a dark soil. Hilgard,^ who lays great stress on the 
agricultural significance of color, considers the mottled 
yellows and reds as indications of poor drainage, since 
such a condition shows that oxidation has been both 
unequal and insufficient. A soil that has a heavy blue 
or mottled blue clay as a subsoil will in most cases be 
greatly benefited by some form of drainage. 

60. Soil and subsoil. — A common distinction is made 
between the surface soil and that which is some distance 
below the surface. This is natural, as the forces of soil 
formation have served to bring about certain distinctions, 
especially in humid regions, which are of importance in 
any consideration of soil fertility and crop growth. Cli- 
matic agencies acting on soil after it has been formed have 
served to intensify these distinctions. The term soil 
is used to designate the top layer of earth, which usually 
extends to the plow line or even deeper. The soil below 
is spoken of as the subsoil, and may be rather variable in its 
depth (Fig. 10). Often the subsoil is divided into the upper 

1 Hiigard, E. W. Soils, pp. 283-285. New York. 1906. 



80 



SOILS: PROPERTIES AND MANAGEMENT 



and the lower subsoil, the upper subsoil being considered 
to extend to about the depth of three feet below the sur- 
face. I^sually, especially in humid regions, there is a 




Fig. 10. — Soil and subsoil, (a), Surface soil with many plant roots; 
(b), subsoil; (c), country rock. 



sharp line of demarcation between the soil and the sub- 
soil, due to differences in the humus content. As organic 
matter accumulates faster at the surface, the soil there 
tends to assume a darker color. Whether the land has 
been tilled or not, this line of separation is fairly marked 
and can usually be located with little difficulty. On 
tilled land, where the surface soil extends to about the 
depth of plowing, the plow line marks the separation of 
surface and subsoil. Where soil samples are being taken 
for soil survey or soil analysis, some arbitrary depth, 
depending on circumstances, is usually established for 
the surface soil. This depth varies from six to twelve 
inches. 
61. Soil and subsoil of humid regions. — In humid cli- 



CLIMATIC AND GEOCHEMICAL RELATIONSHIPS 81 

mates there are usually certain well-defined differences be- 
tween the surface soil and the subsoil, besides the organic 
content already spoken of. The subsoil is usually of a finer 
and heavier character than the surface soil, due to the 
downward movement of the small particles. This tends 
to give the subsoil high retentive power, and may make 
it rather impervious to water. Poor drainage conditions 
may result. A certain amount of retentive power in a 
subsoil is of considerable advantage, in that it aids in 
the storage of water and prevents the excessive leaching 
away of soluble plant-food. jNIoreover, almost all the 
bacterial activities so important in the simplification of 
compounds carrying food constituents are restricted 
to the surface soil. The subsoil, being protected by the 
layers above, has not been subjected to such vigorous 
weathering, and as a consequence its mineral constituents 
are not so available for the use of the crop. The deepen- 
ing of the plow line and a consequent turning-up of the 
subsoil must be carried out very cautiously for the above 
reason. The cropping power of a soil may be markedly 
reduced by the presence of too much of such material on 
the surface at one time. 

The root distribution is restricted largely to the surface 
soil, and this condition determines to some extent the 
larger accumulation of humus therein and also its better 
aeration and drainage. Experiments conducted in Utah ^ 
show that with barley, corn, and clover, from 90 to 96 
per cent of the roots grow in the upper seven inches of 
soil. From experiments made in Kansas ^ and in North 

1 Sanborn, J. W. Roots of Farm Crops. Utah Agr. Exp. 
Sta., Bui. 32. 1894. 

- Ten Eyck, A. M. The Roots of Plants. Kansas Agr. Exp. 
Sta., Bui. 127. 1904. 

G 



82 soils: properties and management 

Dakota/ the roots of such crops as alfalfa were found 
to penetrate to a depth of ten feet, while the small grains 
often showed an extension of their roots to four feet 
below the surface. It must be borne in mind, however, 
that, while some plant roots may penetrate far into the 
subsoil, the main feeding rootlets are restricted largely 
to the surface soil. This is natural, as there they find 
the aeration and drainage essential to normal growth. 
Hilgard ' has shown that plants in arid regions have a 
root extension far beyond that of the same crops under 
humid conditions. The physical conditions of the arid 
subsoil, the larger amount of plant-food, and the better 
aeration, account for such differences. 

62. Soil and subsoil of arid regions. — The subsoils 
in arid or semiarid regions do not exhibit such marked 
contrast to the surface soil as are observed in humid 
climates. In arid soils there is generally no sharp line 
of demarcation between soil and subsoil, the latter being 
as high in humus and in agricultural value as the former. 
Nor is any great textural variation to be observed. The 
latter condition is due to the fact that physical weather- 
ing is dominant in such a region. As a consequence, arid 
soils may be leveled, often excessively, in establishing 
an even surface for the application of irrigation water, 
without any danger of lowering the fertility thereby. 
Such a practice in humid regions would be fatal to the 
further growing of successful crops, at least for a con- 
siderable period of years. 

^ Sheppard, J. II. Root Systems of Field Crops. N. Dak. 
Agr. Exp. Sta., Bui. G4. 1905. 

2 Hilgard, E. W. Soils, Chapter X, pp. 161-187. New York. 
1911. 



CHAPTER VI 
THE .SOIL PARTICLE 

The soil formed by the grinding-iip of rocks and the 
intermixing therewith of small quantities of organic 
matter must be studied physically from the standpoint 
of its particles. These particles, varying in size from 
coarse gravel easily discernible by the naked eye to 
particles so fine as to be invisible under the ultramicro- 
scope, determine very largely the different relationships 
of the soil to the plant. The movement of air in the soil, 
the circulation of water, the rate of oxidation and hydra- 
tion, and the presence and virility of various organisms, 
are determined very largely by the size of the particles 
making up the soil. Texture is the term used to express 
this size of particle. Thus a soil texture may be coarse, 
medium, or fine, indicating that the particles making up 
that soil conform in general to such description. Tex- 
ture is of great importance in soil study and utilization. 

There is hardly any condition exliibited by the soil 
that is not influenced, if not directly determined, by the 
size of the soil particles. A study of plant conditions, 
whether physical or chemical, ultimately leads either 
directly or indirectly to a consideration of soil texture. 
Texture, however, is an element which can be but little 
modified under normal conditions. We have seen how 
a rock can be disintegrated and decomposed into a soil. 
A change in texture has been wrought, but such a process 
demands geologic ages for its fulfillment. In the time 

83 



84 SOILS: PROPERTIES AND MANAGEMENT 

covered by the life of man the necessary forces are not 
active enough to have this effect ; consequently, as far 
as the farmer is concerned the texture of the soil in his 
field is subject to but slight alteration. A sand remains 
a sand and a clay remains a clay, as far as practical con- 
siderations are concerned. Changes in texture may be 
made on a small scale by mixing two soils, but this is not 
practicable in the field. 

63. Soil separates and mechanical analysis. — The 
soil particles, varying in size as they do, may be separated 
into arbitrary divisions, according to their diameters. 
The various groups are designated as soil separates, and 
the process of making the separation and determining 
the percentage of each group present is called mechanical 
analysis. There are a large number of classifications, or 
groupings, of the soil particles, as well as several methods 
of bringing about the actual separation. The grouping 
and method of mechanical analysis most generally used 
in this country is that devised by the United States Bureau 
of Soils. ^ Other methods ^ are more nearly accurate, 
but speed as well as precision is necessary in this work. 
A Swedish classification ^ of soil particles has been adopted 
by the Committee on Mechanical Soil Analysis,^ appointed 

1 Briggs, L. J., and others. Tho Centrifugal Method of Soil 
Analysis. U. S. D. A., Bur. Soils, Bui. 24. 1904. 

^ For a detailed discussion of all methods of mechanical 
analysis, see Wiley, H. W. Agricultural Analysis, Vol. I, 
pp. 195-276. Easton, Pa. 1906. 

' Atterberg, A. Die Mechanische Bodenanalyse uud die 
Klassifikation der IMinerallxiden Sehwedens. Internat. Mitt, 
f. Bodenkunde, Band 11, Heft 4, Seite 312-342. 1912. 

* Sehucht, F. Uber die Sitzung der Internationalen Kom- 
mission fiir die Mechanische und Physikalische Bodenunter- 
suchung in Berlin am 31, October 1913. Internat. Mitt. f. 
Bodenkunde, Band IV, Heft I, Seite 1-31. 1914. 



THE SOIL PARTICLE 



85 



by the Second International Agro-Geological Congress, 
which met in Stockholm in 1910. In simplicity and 
facility of interpretation the last-named grouping seems 
at least equal to that of the Bureau of Soils. Since a 
number of methods of mechanical analysis have been 
devised during the evolution and study of soil separation, 
it is necessary to be conversant with the principles in- 
volved and with at least two or three of the most successful 
modes of procedure. 

64. Principles of mechanical analysis. — The various 
methods of mechanical analysis may be grouped according 
to the agents employed in the separation. The outline is 
as follows : — 



1. Sieve 



Outline of systems of mechanical analysis 

Wet 

Qj. (Used to separate sands in practically all 

jy methods) 



2. Air (Cushman's air elutriator) 
In motion 



3. Water { 



At rest 



Gravity (Schone's elutriator and 

Hilgard's churn elutriator) 
Centrifugal (Yoder's centrifugal 

elutriator) 
Gravity (Osborne's beaker method 

and Atterberg's modified silt 

cylinder) 
Centrifugal (Bureau of Soils 

method) 



In the consideration of such an outline, certain of the 
general methods proposed may be dismissed without 
further parley since they are inadequate for the separation 



9,fi SOILS: PJiOPERTIES AXD MANAGEMENT 

in question. Sieves of all kinds have the one great dis- 
advantage that their meshes cannot be made small enough 
to separate the finer grades of soil. When one considers 
that many soil particles are less than ,005 millimeter in 
diameter, the inadequacy of sieve separation becomes 
apparent. However, sieves may be used in connection 
with other methods as an easy way of dealing with the 
larger soil particles. Air in motion ^ is inadequate, as 
it can be used only for very fine particles. Even with 
these the separation is slow and inaccurate, because of 
the tendency of the dry particles to cohere. These two 
methods have therefore been largely abandoned as dis- 
tinct methods, and water is used as the medium of separa- 
tion in all the modern systems of mechanical analysis. 

The principle involved in the subsidence of soil particles 
in water, whether the force of gravity or centrifugal 
force is utilized, is recognized by every one. When 
fragments of rock or soil are suspended in water, they 
tend to sink slowly, and it is a well-recognized fact that 
other things being equal, the rate of settling depends 
on the size of the particle. As the particle is decreased 
in size, its weight decreases faster than the surface ex- 
posed to the buoyant force of the water. As a conse- 
quence, the rapidity with which the soil particles settle 
is proportional to their size. The suspension of a sample 
of soil would therefore be the first step in mechanical 
separation by water ; the second step would be subsidence 
and the withdrawal of each successive grade of particles 
as it slowly settled ; the third step would be determina- 
tion of the percentage of each grade, or group, of particles 

1 Cushman, A. S., and Hubbard, P. Air Elutriation of 
Fine Powders. Jour. Araer. Chem. Soc, Vol. 29, No. 4, pp. 
589-597. 1907. 



THE SOIL PARTICLE 



87 



f/ 



as based on the original sample. This is precisely what 
every method of mechanical analysis in which water is 
utilized aims to do, although often the apparatus and 
technique are excessively complicated, 

65. Mechanical analysis by water in 
motion. Schbne's elutriator. — Any ap- 
pliance that is designed to separate 
particles of different sizes by water in 
motion may be designated as an elutria- 
tor. One of these, commonly used in 
Europe, is called Schone's elutriator.^ 
This utilizes hydraulic force. In it the 
upward current of water ascends a coni- „ 
cal glass tube (see Fig. 11) from a ^ T 
narrow curved inlet tube below. The 
soil sample present in the inlet tube is 
kept agitated by the current. It is evi- 
dent that by regulating the rate of flow 
of the water, different sizes of particles 
will be carried away over the top of 
this conical glass tube. Thus by a gentle 
flow only fine grades will be. separated, 
while by increasing the current larger 
and still larger particles will be carried 
upward against the force of gravitv. ^ „ , , 

%^, ^ , , . . ^ • . Fig. U. — Schone's 

Ihere are three objections to this elutriator for me- 
method : first, the entrance tube mav chamcal soil 

, 1111 11 analysis with 

become clogged, and, unless a very small water in motion. 



1 Schone, E. Ueber Sehlammanalyse. Bui. Soe. imperiale 
des Naturalistes de Moscow, 40, Part 1, p. 324. 1867. Uber 
Sehlammanalyse und einen neuen Schliimmapparat. Berlin, 
1867. Also see Wiley, H. W. Agricultural Analysis, Vol. I, 
pp. 231-241. Easton, Pa. 1906. 



88 



SOILS: PROPERTIES AND MANAGEMENT 



quantity of soil is used, the mass is not kept properly 
agitated ; secondly, convex currents are set up in the 
conical glass tube, which vitiates the results ; and, thirdly, 
the separate particles tend to coalesce into granules. It 
is evident that in any separation of soil particles all 
granulation must be avoided. This is usually accom- 
plished by shaking or boiling the 
sample previous to the determi- 
nation. The tendency toward 
granulation during the process 
of separation itself is fatal to 
accuracy, as compound particles 
carrying a large number of small 
grains would fail to pass over 
at water-current velocities cor- 
responding to their component 
parts. 

66. Hilgard's chum elutriator. 
— The errors of the Schone ap- 
paratus are obviated to some 
extent by Hilgard's,' the prin- 
ciple of operation remaining ex- 
actly the same. In Hilgard's 
elutriator the deflocculated soil 
] sample is introduced into the 




Fig. 12. — Hilgard's churn base of a cylindrical tube (see 

elutriator for mechanical ^i 12) in \vhich is placed a 
sou analysis of particlos • ,, i • • m, • 

above .01 mm. in diameter, rapidly revolving stirrer. I his 
(e), Intake; (p), stirrer; is fJesigned to Counteract convex 

(c;, screen ; (a), separating 

chamber; (o), outlet tube. Currents and to prevent the 

' Hilgard, E. W. M(>Miods of Physioal and Chemioal Soil 
Analv.sis. Ann. Rept. California Agr. E.xp. Sta., pp. 241-257. 
1891-1892. 



THE SOIL PARTICLE 89 

formation of compound particles. A screen placed just 
above the stirrer serves to prevent the whirling motion 
from being communicated to the ascending column of 
water in which the separation occurs. The various grades 
in the separation are regulated by the rate of water flow. 
^Yith this apparatus it is necessary to remove the finer 
particles below .01 mm. in diameter by subsidence 
previous to the determination. 

While this method is very nearly accurate and will 
give a separation of the various grades such as is impossible 
with most other methods, it is impracticable in ordinary 
soil work. The large quantity of water which is used 
in carrying over each grade, and which of course must 
be evaporated before the sample can be weighed, is the 
first objection. The length of time necessary for the 
separation, and the cost of the apparatus, are two addi- 
tional objections urged against it. As mechanical analysis 
is used largely in determining soil texture, rapidity and 
ease of operation are of more importance than the ex- 
tremely accurate separation of the particles. 

67. Yoder's centrifugal elutriator. — One of the ob- 
jections to the methods already described is the length 
of time necessary for a determination. This is due to 
the fact that very fine particles subside in water very 
slowly. In order to hasten the separation, Yoder ^ 
devised a machine in which hydraulic force may be 
supplemented by a centrifugal pull. This ingenious 
apparatus consists of an elutriator bottle (see Fig. 13) 
mounted in a centrifuge. The muddy water is introduced 
into the bottle at the center of the centrifuge. It then 
passes to the bottom of the bottle and back again to the 

1 Yoder, P. A. A New Centrifugal Soil Elutriator. Utah 
Agr. Exp. Sta., Bui. 89. 1904. 



90 



SOILS: PROPERTIES AND MANAGEMENT 



outlet, carrying with it a sediment the size of which 
depends on the rate of water flow and the strength of 
the centrifugal force. The bottle is so designed that 
particles in all parts of the separating chamber are sub- 
jected to the same force, no matter what their distance 




Fig. 13. — Separatory bottle of Yoder's centrifugal elutriator. (B), Bottle ; 
((•), intake ; («), tube for conducting liquid to bottom of separatory 
bottle; (o), outlet; (C), centrifuge; (w), counterpoise. 

from the center of the centrifuge may be. The apparatus 
can be used only for separating particles less than .03 
millimeter in diameter. It is open to the same objections 
that apply to Hilgard's machine, besides being very much 
more complicated and delicately adjusted. It is too 
costly an apj)aratus for ordinary work. 

68. Mechanical analysis by water at rest. Osborne's 
beaker method. — One of the earliest and most nearly 
accurate methods to be perfected was the separation of 
the various grades of soil by simple subsidence in a column 
of still water. This is commonly spoken of as the Os- 
borne beaker method.^ The determination is very 
simple. The soil sample is first fully deflocculated and 
thrown into suspension, each particle functioning sepa- 
rately. Beakers are commonly used as containers, but 

' Osborne, T. B. Methods of Mechanieal Soil Analysis. Ann. 
Kept. Connecticut Agr. E.xp. Sta., 1886, pp. 141-158; 1887, pp. 
144-1G2; 1888, pp. 154-157. 



THE SOIL PARTICLE 91 

any vessel that is relatively deep will do for the deter- 
mination. The larger particles, or sand grains, will of 
course settle first, and the finer silts and clays may be 
decanted oft'. As the sands carry finer particles down 
with them, the suspension and subsidence must be re- 
peated a number of times. The finer particles, separated 
thus and decanted, may be further subdivided in the 
same manner. The time necessary for such decantation 
as will leave in suspension only particles below a given 
size is determined by the examination of a drop of the 
suspension under a microscope fitted with an eyepiece 
micrometer. In this way the size of the particles decanted 
may be accurately measured. 

The three steps in this method of separation are : 
deflocculation of the sample; separation by successive 
subsidence and decantation; and evaporation to dryness 
of the separates and their calculation to a percentage 
based on the original sample. The method, however, is 
slow, as the time necessary for each subsidence of the 
finer particles is very great and the number of individual 
subsidences is large. Neither is the method capable of 
the refinement of separation which is possible with cer- 
tain of the elutriators. As a consequence it has been 
superseded by methods that utilize centrifugal force for 
the finer separations while retaining gravity for removing 
the various grades of sand. 

69. Atterberg's modified Appiani ^ silt cylinder (Fig. 
14). — This method ^ is similar to the beaker method in 

1 Appiani, G. Ueber einen Schlammapparat fiir die Analyse 
dor Boden- imd Thonarten. Forsoh. a. d. Gebiete d. Agri- 
Physik, Band 17, Seite 291-297. 1894. 

- Atterberg, A. Die JMeehanische Bodenanalyse und die 
Klassifikation der Mineralboden Sehwedens. Internat. Mitt, 
f. Bodenkunde, Band II, Heft 4, Seite 312-342. 1912. 



92 



SOILS: PROPERTIES AND MANAGEMENT 




general principle, but a special apparatus is employed by 
means of which the various grades obtained by sedimenta- 
tion are siphoned oti" instead of decanted. The cylinder is 
really a modified Wahnschaft'e cylinder/ such as was 
used in early soil analyses for drawing ofi' the various 
suspensions except that the siphon is placed outside the 
cylinder instead of inside. 

The cylinder (die Schliimmapparat) 
as used by Atterberg is about 25 cen- 
timeters high, with a glass pedestal 
and a ground glass stopper. It is 
graduated at 5, 10, 15, and 20 cen- 
timeters upward from the bottom. 
The same distance is divided also 
into 16 divisions at the left of the 
first graduation. The latter gradua- 
tion is used in the separation of the 
clay (Schlamm), so that the height 
of the sedimenting column may be 
regulated according to the time 
available for the settling process. 
An outside siphon, 4 to 5 milli- 
meters wide, is attached to the cylin- 
der at the bottom for the drawing 
of the liquid when the sedimenta- 
tion is complete. The top of this 
siphon is opposite the 5-centimeter 
mark on the cylinder. Cylinders 
of this size are used only for tlie separation of particles 
below .2 millimeter in diameter ; for larger particles a 
somewhat taller cylinder is used, with a siphon of the 

^ Wiley, H. W. Agricultural Analysis, pp. 205-207. Easton, 
Pa. 190(j. 




Fig. 14. — AttcrbeiK's 
silt cylinder for the 
mechanical analysis 
of soil by subsidence. 



THE SOIL PARTICLE 93 

same width as for the finer particles. The graduation of 
the eyhnder and its diameter are the same as described 
above. 

A 20-gram sample of soil is used with this apparatus, 
anfl deflocculation is brought about by means of a stiff 
brush. The sample is reduced to a paste in a porcelain 
dish, and then, by alternate working with the brush 
and decanting, all the particles are thrown into separate 
suspension. A deflocculating chemical is used in humus 
soils, in order to hasten the process and counteract the 
effect of the organic matter. As in the beaker method, 
the size of the various grades of separation may be varied 
according to the will of the operator. 

70. Centrifugal soil analysis. — Of the centrifugal 
methods used in mechanical analysis, that employed by 
the United States Bureau of Soils ^ is the most successful. 
A 5-gram sample of well-pulverized soil is put into a 
shaker bottle of about 250 cubic centimeters capacity 
(see JFig. 15). This bottle is filled about two-thirds 
full of water, so that in shaking the disintegrating force 
of the liquid may be utilized. A few^ drops of ammonia 
are added, to dissolve the organic matter and to make 
deflocculation easier. The sample is then agitated in 
the bottle until disintegration is complete. This period 
ranges from five to twenty hours, depending on the 
sample. 

The separation of the silt and the clay from the sands 
is made in the shaker bottle by simple subsidence, the 
time for decantation being determined by a microscopic 
examination of a drop of the suspension. The silt and 

1 Fletcher, C. C, and Bryan, H. Modifications of the 
Method of Soil Analysis. U. S. D. A., Bur. Soils, Bui. 84. 
1912. 



94 



SOILS: PROPERTIES AND MANAGEMENT 



the clay are decanted directly into a test tube fitted into 
a centrifuge (see Fig. 15). Whirling at the rate of 800 to 
1000 revolutions a minute will cause the subsidence of 
the silt to the bottom of the test tube in a few minutes. 
The clay is then decanted. The microscope is necessary 
here, in order to determine when the settling of the silt 
is complete. As small particles tend to cling to the 
larger particles, the entire operation must be repeated 




Fig. 15. — Apparatus for centrifugal mechanical analysis of soil, show- 
ing shaker bottle, shaker, centrifuge, and test tube. 



several times ; therefore the jirocesses of gravity sub- 
sidence and centrifugal subsidence are carried on side by 
side, material being constantly poured from the shaker 
bottle into the centrifuge tubes and from the test tubes 
into the receptacles for the clay. 

The centrifuge is usually large enough to allow the 
separation of several duplicate samples at once. The 
various sei)arates made by this method are dried and 



THE SOTL PARTICLE 95 

weighed. The sands, which are obtained in bulk, are 
further separated by sieves into the grades desired. 
Where a large quantity of organic matter is present, it 
must be determined and included in the final report on 
the sample. 

This method of mechanical analysis as perfected by 
the Bureau of Soils has been very generally adopted by 
soil workers. It has many advantages over other methods. 
In the first place, it is rapid, often requiring only hours 
where other methods take days for completion ; secondly, 
it is simple, and the technique of the separation is easily 
acquired ; thirdly, in the decantations no very large 
amount of water is accumulated with the separates, 
except for the clay, and thus the time and cost of evapora- 
tion is eliminated. The clay, moreo^'er, may be as ac- 
curately determined by difference as by direct methods, 
thus allowing a further saving of time. The cost of the 
equipment for this method is low. The apparatus itself 
is simple, and is carried by all standard chemical com- 
panies. The same cannot be said of the various elutriator 
mechanisms. While the method is accurate only within 
one per cent, it is sufficiently precise for practical pur- 
poses, especially in class determination, for which me- 
chanical analysis is generally utilized. 

71. Classification of soil particles. — With the large 
number of different methods of mechanical soil analyses 
there has arisen a large variation in textural groupings 
expressed in diameter of particles. This would naturally 
occur because of the differences in degree of refinement 
which the various methods of separation allow, and also 
because of the uses which the investigators wished to 
make of such analyses. Some of the best-known group- 
ings are given below : — 



96 



SOTLS: PR0PEPTIE8 AND MANAGEMENT 



Various Textural Classifications used in the Mechani- 
cal Analyses of Soils. Expressed in Diameter of 
Particles in Millimeters 



Separate 


Osborne ' 


HiLGARD 2 


Bureau of 
Soils' 


English* 


Atterberg ' 


1 


3.000 


3.000 


2.000 


1.000 


20.000 


2 


1.000 


1.000 


1.000 


.200 


2.000 


3 


.500 


.500 


.500 


.040 


.200 


4 


.250 


.300 


.250 


.010 


.020 


5 


.050 


.160 


.100 


.002 


.002 


6 


.010 


.120 


.050 






7 




.072 


.005 






8 




.047 








9 




.030 








10 




.025 








11 




.010 








12 




.010 









Of these classifications only three need claim our atten- 
tion — that of the Bureau of Soils, that of Hall and 
Russell (the English classification), and that devised by 
Atterberg. These represent the groupings used in ex- 
pressing mechanical soil analyses in the United States, 



1 Osborne, T. B. Methods of Mechanical Soil Analysis. 
Ann. Rept. Connecticut Agr. Exp. Sta., 1886, pp. 141-158; 
1887, pp. 144-162; 1888, pp. 154-157. 

2 Hilgard, E. W. Methods of Physical and Chemical Soil 
Analysis. Ann. Rept. Cahfornia Agr. Exp. Sta., 1891-1892, 
pp. 241-257. 

' Briggs, L. J., and others. The Centrifugal IMethod of 
Soil Analysis. U. S. D. A., Bur. Soils, Bui. 24. 1904. 

* Hall, A. D., and Russell, E. J. Soil Surveys and Soil 
Analyses. Jour. Agr. Science, Vol. IV, part 2, pp. 182-223. 
1911. 

* Atterberg, A. Die Mechanische Bodenanalyse und die 
Klassifikation der Mineralboden Schwedens. Internat. Mitt, 
f. Bodenkunde, Band II, Heft 4, Seite 312-342. 1912. 



THE SOIL PARTICLE 



97 



in England, and in Continental Europe, respectively. 
As to which is the best for an interpretation and ex- 
pression of textural qualities it is difficult to say. They 
are all arbitrary, yet they are all extremely useful. 
It therefore seems immaterial which one is employed. 
It would be better, of course, if the classification were 
uniform for all countries; correlation of soil properties 
would then be easier. 

72. Bureau of Soils classification. — As the grouping 
established by the United States Bureau of Soils is met 
with in all of our soil literature, and as it is really the 
standard classification for this country, a closer considera- 
tion of it may be profitable. The discussion of the 
properties exhibited by the various separates, and of the 
interpretation and value of a mechanical analysis, will 
therefore be made with this classification as a basis. By 
way of illustrating the grouping and the mode of ex- 
pressing a mechanical analysis the results obtained from 
two distinctly different soils are given below : — 

Mechanical Analyses ' of a Dunkirk Fine Sandy Loam 
AND a Dunkirk Clay 



Separate 



Fine gravel . 
Coarse sand . 
Medium sand 
Fine sand 
Very fine sand 
Silt . . . 
Clay . . . 



Size in 
Millimeters 



2-1 

1-.5 

.5-.25 

.25-. 10 

.10-.05 

.05-.005 

below .005 



Fine Sandy 
Loam 



1 

2 
3 
22 
35 
27 
10 



Clay 



% 
1 

2 
2 
6 
7 
39 
43 



1 Soil Survey Field Book, pp. 152, 154. 
Soils. 1906. 



U. S. D. A., Bur. 



98 SOILS: PROPERTIES AND MANAGEMENT 

73. Physical character of the separates. — It is im- 
mediately apparent that as these groups vary in size they 
must exliibit properties, especially physical ones, which 
are widely different. These properties should in turn 
be imparted to the soil of which the separates form a 
part. If we are conversant with these various values, a 
mechanical analysis should reveal to us at a glance cer- 
tain soil conditions which may or may not be conducive 
to the best plant growth. 

The clay particles are very minute ; many of them are 
so small as to be invisible under the ultramicroscope. 
They are really shreds and fragments of minerals, and 
are jagged and angular in outline. They are highly 
plastic, and when rubbed together they become sticky 
and impervious. They shrink much on drying, with the 
absorption of considerable heat. On being wet again 
they swell wdth the evolution of the heat already taken 
up. Many of the particles exlaibit the Brownian move- 
ment and will remain in suspension for an indefinite 
period. The finer part of the clay makes up a ]3orti()n of 
that indefinite group of material hi the soil called colloids, 
which because of their fineness of division (molecular 
complexes) exhibit certain well-defined properties, of 
which adsorption of moisture and salts in solution, and 
high plasticity and cohesion, are the most important 
from a soil standpoint. Silt exhibits the same qualities 
as clay, but to a much less marked extent. The presence 
of clay in a soil imparts to it a heavy texture, with a 
tendency to slow water and air movement. Such a soil 
is highly plastic, but becomes sticky when too wet and 
hard and cloddy when too dry. The expansion and the 
contraction on wetting and drying are very great. The 
water-holding capacity of a clay soil is high. 



THE SOIL PARTICLE 99 

The sands and the gravel, because of their sizes, func- 
tion as separate particles. They are irregular and rounded, 
the continual rubbing that they have received being 
sufficient to have effaced their angular character. They 
exhibit very low plasticity and cohesion, and as a con- 
sequence are little influenced by changes in water content. 
Their water-holding capacity is low, and because of the 
large size of the spaces between each separate particle 
the passage of water is rapid. They therefore facilitate 
drainage and encourage good air movement. In all 
the grades of sand the separate particles are visible to 
the naked eye, a condition impossible with the silt and 
clay groups. Soil containing much sand or gravel, 
therefore, is of an open character, possessing good 
drainage and aeration, and is usually in a loose friable 
condition. 

74. Mineralogical characteristics of the separates. — 
From the mineralogical standpoint there are usually 
considerable differences in the soil separates. These 
differences would naturally be expected to occur par- 
ticularly in residual soils, because of the dift'erentiating 
tendencies of weathering. Quartz would naturally per- 
sist, and because of its sIoav solubility would very soon 
make up most of the larger soil grains. Other minerals, 
such as the feldspars, hornblende, augite, and the like, 
being less persistent as the law of mineral resistance 
has already taught us, would be worn to fine shreds 
and be found as the main constituents of the silts 
and the clays. The following data sustain this as- 
sumption regarding the mineralogical characteristics of 
some of the soil groups as designated by the Bureau of 
Soils as well as furnish some interesting comparisons of 
some important soil provinces : — 



100 SOILS: PROPERTIES AND MANAGEMENT 

General Mineralogical Composition of the Sands and 
Silts op Various Soil Provinces of the United States ' 



Soil 


No. OP 
Samples 


Minerals other than 
Quartz in 




Sands 


Silts 


Residual 

Glacial and loessial . . 

Marine 

Arid 


12 
6 
4 
3 


15% 
12% 

5% 
37% 


21% 
15% 

8% 
42% 



It is to be seen immediately that in every ease the 
silt carries a larger quantity of the important soil-forming 
minerals and a smaller quantity of quartz than does the 
sand. This reveals at least one of the reasons for the 
greater fertility and lasting qualities of fine-textured soils 
as far as agricultural operations are concerned. It is 
important to note, however, that, although quartz is 
the predominating mineral in sands, all the common 
soil-forming minerals are usually accessory. This merely 
serves to again emphasize the fact that all soils contain 
all the common minerals found in soil-forming rocks. 

It is also interesting to note the general differences 
exhibited by the various soil provinces. The residual, 
glacial, and coastal plain soils possess minerals other 
than quartz in the order named. In the marine soils, 
in particular, this difference has largely come about by 
the disintegration and leaching that these soils have 
undergone during their formation. The arid soils, due 
to the suppression of chemical weathering and the activity 

* McCaughey, W. G., and William, H. F. The Microscopic 
Determination of Soil-Forming Minerals. U. S. D. A., Bur. 
of Soils, Bui. 91. 1913. 



THE SOIL PARTICLE 



101 



of the physical agents, exhibit smaller quantities of free 
ciuartz. The silica in such soils is held as complex sili- 
cates, which very largely carry the elements that are so 
important in plant development. 

Although these data are based on but a few samples, 
they are so concordant with what would naturally be 
expected that these general conclusions cannot be avoided. 

75. The chemical constitution of soil particles. — The 
mineralogical examination of soils has revealed a larger 
percentage of such minerals as feldspars, mica, horn- 
l)lende, and the like, in the finer separates. A larger 
percentage of the important plant-food elements would 
therefore be expected in those groups. The following 
data,^ compiled from work performed by the United 
States Bureau of Soils, substantiate this assumption : — 

Chemical Composition of Various Soil Separates 





NuM- 


Percentage or 


Percentage op 


Percentage op 


Soils 


BEROP 

Sam- 
ples 


P2O5 IN 


K2O IN 


CaO IN 




Sand 


Silt 


Clay 


Sand 


Silt 


Clay 


Sand 


Silt 


Clay 


Crystalline residual 


3 


.07 


.22 


.70 


1.60 


2.37 


2.86 


.50 


.82 


.94 


Limestone residual 


3 


.28 


.23 


.37 


1.46 


1.83 


2.62 


12.26 


10.96 


9.92 


Coastal plain 


7 


.03 


.10 


.34 


.37 


1.33 


1.62 


.07 


.19 


.55 


Glacial and loessial 


10 


.15 


.23 


.86 


1.72 


2.30 


3.07 


1.28 


1.30 


2.69 


Arid soils 


2 


.19 


.24 


.45 


3.05 


4.15 


5.06 


4.09 


9.22 


8.03 



It is seen that on the average the soils with finer particles 
are richer in phosphoric acid, potash, and lime, than 
those of coarser texture, the only exception in this case 
being in the lime of the residual limestone soils. The 
arid soils present a less marked difference in the sands. 



' Failyer, G. H., and others. The Mineral Composition 
of Soil Particles. U. S. D. A., Bur. Soils, Bui. 54. 1908. 



102 SOILS: PROPERTIES AND MANAGEMENT 



silts, and clays than the representatives of the other 
soil provinces ; this is true also of the glacial soils, but 
to a less degree. Under such conditions of weathering 
the sands have not as yet been depleted of their stores 
of essential elements. Average data compiled from a 
number of soil analyses by HalV presented below, tend 
to corroborate the data already noted and that obtained 
by Loughridge - of California : — 

Composition of Soil Separates 





SiOj 


AbO, 


FesOa 


CaO 


MgO 


K2O 


P2OS 


Coarse sand (1-.2 mm.) . 


93.9 


1.6 


1.2 


.4 


.5 


.8 


.05 


Fine sand (.2-. 04 mm.) 


94.0 


2.0 


1.2 i .5 


.1 


1.5 


.1 


Silt (.04-.01 mm.) . . . 


89.4 


5.1 


1.5 I .8 


.3 


2.3 


.1 


Fine silt (.01-.002 mm.) . 


74.2 


13.2 


5.1 


1.6 


.3 


4.2 


.2 


Clay (Below .002 mm.) . 


53.2 


21.5 


13.2 


1.6 


1.0 


4.9 


.4 



76. Value of a mechanical analysis. — It is now evi- 
dent that the proper interpretation of a mechanical 
analysis throws considerable light on the probable physical 
and chemical properties of a soil. To the trained ob- 
server the preponderance of sand or clay signifies certain 
physical properties which may affect the plant not only 
mechanically, but physiologically as well, through varia- 

1 Hall, A. D., and Russell, E. J. Soil Surveys and Soil 
Analyses. Jour. Agr. Science, Vol. IV, Part 2, p. 199. 1911. 
Also a Report of the Agriculture and Soils of Kent, Surrey', and 
Sussex. Board of Agriculture and Fisheries. 1911. 

"^ Loughridge, R. H. On the Distribution of Soil Ingredi- 
ents among Sediments Obtained in Silt Analyses. Amer. 
Jour. Sci., Vol. VII, p. 17. 1874. 

In this connection see also Puchner, Dr. Uber die Ver- 
tielung von Nilhrstoffen in den Verschieden Feinen Bestaudteilen 
des Bodeu. Landw. Ver. Stat., Band 66, Seite 463-470. 1907. 



THE SOIL PARTICLE 103 

tioiis in air and water movements. The chemical phases 
of snch an interpretation are also worthy of considera- 
tion, as the proportion of the various separates determines 
whether the essential plant-food elements will be present 
in sufficient quantities to permit normal crop growth. 
Thus in a general way the mechanical analysis of a soil 
not only enlightens us as to the general properties of a 
given soil, but is to some extent a criterion of agricultural 
value and crop adaptation. Some authors ^ maintain 
that in the investigation of any soil a mechanical analysis 
should first be made, as such an analysis throws so much 
light on the general qualities of a soil. 

77. Soil class. — Class is a term used in relation to 
the texture, or size of particles, of a soil. Class differs 
from texture, however, in that it has reference rather to 
the particular properties exhibited by a soil than to any 
absolute grain size. As soils are not made up of particles 
of the same size, a blanket term is needed which will not 
only give an idea of the texture of the soil, but also name 
it in such a manner as to reveal general peculiarities and 
properties. We may have any number of classes, de- 
pending on the sizes of the soil grains carried. 

These class names liave originated through long cen- 
turies of agricultural operations, but of late they have 
been more or less standardized because of the necessity 
of a definite nomenclature. In general the names used 
for the soil classes are the same as are used in mechanical 
analyses to designate the soil separates. This is rather 
unfortunate, but it obviates the increase of technical terms 
and a little care will prevent confusion in this regard. 

Another word introduced by common usage is loam. 

' Hall, A. D., and Russell, E. J. Soil Surveys and Soil 
Analyses. Jour. Agr. Science, Vol. IV, Part 2, p. 199. 1911. 



104 SOILS: PROPERTIES AND MANAGEMENT 

Loam, from the technical standpoint, refers to a soil 
possessing in about equal amounts the properties im- 
parted by the various separates. If, however, we have 
practically the same condition but with one size of particle 
predominating, the name of that particular separate is 
prefixed, giving still more data regarding the soil in 
question. Thus a loam in which clay is dominant will 
be classified as a clay loam. In the same way we may 
have a sandy loam, a sandy clay loam, a gravelly sandy 
clayey loam, and so on. The number of soil classes that 
may occur is therefore rather large, ranging from coarse 
gravel, through the various grades of sands, to silts and 
clays. 

A few of the common classes, with their mechanical 
analyses, are listed below : — 

Mechanical Composition of Various Soil Classes ^ 



Coarse sands . 
Sands . . •. 
Fine sands 
Sandy loams . 
Fine sandy loams 
Loams . 
Silt loams . . 
Sandy clays . 
Clay loams 
Silty clay loams 
Clays . . . 



a m 
n i' 

I' 



135 
401 
511 

1141 
934 
659 

1268 
162 
718 
765 

1970 



12 
2 
1 
4 
1 
2 
1 
2 
1 

1 



31 
15 
4 
13 
3 
5 
2 
8 
4 
2 
3 



>0Q 



19 


20 


23 


37 


10 


57 


12 


25 


4 


32 


5 


15 


1 


5 


8 


30 


4 


14 


1 


4 


2 


8 



6 
11 
17 
13 
24 
17 
11 
12 
13 
7 
8 



7 
7 
7 
21 
24 
40 
65 
13 
38 
61 
36 



b 
5 
4 
12 
12 
16 
15 
27 
26 
25 
42 



1 Whitney, M. The Use of Soils East of the Great Plains 
Region. U. S. D. A., Bur. Soils, Bui. 78, p. 12. 1911. 



THE SOIL PARTICLE 105 

It is evident that a mechanical analysis of a soil is 
nothing more or less than an expression of class, and 
the inferences that may be derived from either are 
the same. This leads to a consideration of class deter- 
mination. 

78. Determination of class. — The common method 
of class determination is that employed in the field. It 
consists in examination of the soil as to color, an estima- 
tion of its humus content, and, especially, a testing of 
the " feel " of the soil. Probably as much can be judged 
as to the texture and class of a soil by merely rubbing it 
between the thumb and the fingers as by any other 
superficial method. This is a method used in all field 
operations, especially in soil survey work. The accuracy 
of the determination depends largely on experience. 
Inaccuracies are likely to occur in distinguishing between 
the various finer grades of soil ; for this reason more 
nearly exact methods are necessary at times, especially 
in checking soil survey work or in carrying out investiga- 
tions in which absolute accuracy is required. 

As a mechanical analysis of a soil is really a percentage 
expression of texture, it presents an exact method for 
class determination. For detailed work somewhat com- 
plicated tables ^ have been arranged ; but the following 
diagram (Fig. 16), devised by Whitney,^ presents a simple 
method for the identification of a soil from a mechanical 
analysis. The convenience of this triangular representa- 
tion may be tested by the use of the average analyses, 
already presented on a previous page. 

>Bur. of Soils, Soil Survey Field Book, p. 17, U. S. D. A., 
Bur. Soils. 1906. Also, Bur. Soils, Bui. 78, p. 12. 1911. 

- Whitney, M. The Use of Soils East of the Great Plains 
Region. U. S. D. A., Bur. Soils, Bui. 78, p. 13. 1911. 



100 SOILS: PROPERTIES AND MANAGEMENT 




lO so JO ■aO so 60 70 80 yo l0O9(> 



Fig. 16. — Diagram for the determination of soil class from a mechani- 
cal analysis. 



79. The significance of texture and class. — Soil 
texture and class are the basis for all soil consideration, 
whether regarding some specific property or a general 
condition such as crop adaptation. No matter what the 
phase of soil study may be, texture and class are sure 
to have some important influence and nnist be included 
in the investigation. From observations in practice, 
certain crops have been found to be adapted to certain 
kinds, of soil — as clay loam for wheat, silt loam for 
corn, loam or sandy loam for potatoes, clay or clay loam 
for timothy, and so on. Two authors ^ have determined 
the mechanical qualities of soils well adapted to certain 
crops. An average of their analyses is given below : — 



» Hall, A. D., and Russell, E. J. Soil Surveys and Soil 
Analyses. Jour. Agr. Science, Vol. IV, Part 2, p. 207. 1911. 



THE SOIL PARTICLE 



107 



The Mechanical Analysis of Specific Crop Soils 





Wheat 


Barley 


Potato 


Hop 


Fruit 




(9 samples^ 


(9 samples) 


(8 samples) 


(7 samples) 


(6 samples) 


Fine gravel 


1.4 


1.2 


.9 


1.2 


1.0 


Coarse sand . 


3.7 


18.3 


20.1 


4.8 


6.8 


Fine sand . . 


24.5 


32.0 


43.5 


33.8 


42.0 


Silt .... 


23.0 


18.2 


11.0 


28.8 


23.3 


Fine silt . .' 


12.8 


8.0 


6.4 


8.7 


7.3 


Clay . . . 


20.0 


11.9 


9.7 


12.1 


10.9 



The soil particle can thus be seen to function in no 
insignificant manner regarding plant conditions. Its 
size, its physical relationships, its chemical composition, 
and the conditions imposed by a preponderance or a 
limitation in its various grades, are of vital importance. 
Soil texture and soil class, therefore, are terms of constant 
usage in soil discussion and study, whether the viewpoint 
is practical or purely theoretical. 



CHAPTER VII 
SOME PHYSICAL PROPERTIES OF THE SOIL 

While texture is of great importance in the (letennina- 
tion of the physical and chemical nature of a soil, it is 
evident that the arrangement of the particles also exerts 
considerable influence. The term texture refers to the 
size of the soil particles; the term structure is used in 
reference to their arrangement, or grouping. It is at 
once apparent that certain conditions — such, for ex- 
ample, as air and water movement, heat transference, 
and the like — will be as much- affected by structure 
as by texture. As a matter of fact, the great changes 
wrought by the farmer in making his soil better suited 
as a foothold for plants are structural changes rather 
than changes in texture. The compacting of a light 
soil or the loosening of a heavy soil is merely a change 
in arrangement of the soil grains. It is of interest, there- 
fore, to ascertain the probable arrangement of the particles 
in any soil. 

80. Arrangement of soil particles (Fig. 17). — In any 
consideration it is the easier way to advance from the 
simple to the complex. Therefore in the explanation of 
structural relationships a theoretical condition will be dealt 
with first, after which the discussion will proceed to the 
intricate condition existing in the soil. Assuming that 
this theoretical condition consists in spherical particles 
all of the same size, we find these particles susceptible 

108 



ROME PHYSICAL PROPERTIES OF THE SOIL 109 

to two different arrangements: (1) in columnar order, 
witli each particle touched in four points by its neighbors ; 
and (2) the oblique, in which each particle is in contact 
with six of its neighbors. The possible pore space in 
the first case is 47.64 per cent, while that in the second 
case is 25.95 per cent. The amount of this pore space 
is uninfluenced by the size of the particles, provided they 
are round and all of the same volume. 



►-# 


jj 


J 


►"^ 


^ 


^ 


►-% 


•^ 


3 


b. JiL 


J. 


2 



'\ 


% 




f 


\ w 




^ 


^ 


M( 


t 




i 


V ^ 




^ 


\ 


\ 


M 




i 


\ ^i 




'M 


^ 


r \ 


W 




i 


\£ 




'£ 


■^ 




Fig. 17. — Ideal arrangements of spherical particles, showing, from left 
to right, columnar, oblique, compact, and granular orders. 



To any one of practical experience it is a well-knowii 
fact that the soil particles are not homogeneous as to 
size, and neither do all the particles function as simple 
grains, being gathered together in groups called granules, 
or crimibs. A small particle of soil may be made up of 
a number of very small grains. This will modify the 
ideal condition as described above, giving two additional 
conditions — first, a mixture of spherical grains of differ- 
ent sizes, and, secondly, a condition in which the large 
grains are complexes made up of numerous small particles. 
A mixture such as is presented by the first of these con- 
ditions, in which the small grains fit in between the 
larger ones, will result in a reduction of pore space. The 
pore space will fall below 25.95 per cent and approach 
zero. A real soil having such restricted pore space is 



110 SOILS: PROPERTIES AND MANAGEMENT 

designated as l)eing in a puddled condition. This con- 
dition is detrimental to i)lant growth, for it not only 
impedes root development and extension, but also pre- 
vents the circulation of air and water, a function necessary 
for proper soil sanitation. In the second condition an 
increase in pore space must occur, as each large grain 
presents considerable internal air space. If the granules 
as well as their component particles were arranged in 
columnar order, the pore space would reach the high 
percentage of 72.58. Under natural conditions, then, 
the pore space might range from zero plus to about 72 
per cent. 

However, not oidy are the particles of a normal soil 
not of the same size, but they are far from round. A 
soil, as already demonstrated, ordinarily presents varying 
amounts of particles, ranging in size from stone and 
coarse gravel to the very finest clay. These particles 
may also differ in shape, varying from almost perfect 
spheres to flakes, chips, and fragments of every con- 
ceiva])le form. Therefore the laws that apply to the 
ideal condition will hold only in a general way in a normal 
soil. It is evident, first, that the more compact the 
soil, the less is the pore space ; secondly, that it is possible 
to so manipulate a soil as to work the small particles in 
between the larger ones and create an impervious or 
puddled condition ; and, thirdly, that by the forming 
of granules the pore space of a soil may be increased to 
a high percentage. 

From the standpoint of size and arrangement of particles 
there are really two classes of soils, those of single grain 
structure and those that are granular. In the former 
each particle functions separately. In order to do this 
the particles must be large. This condition is found in 



fiOME PHYSICAL PROPERTIES OF THE SOIL 111 



sand. In such soil would naturally be found also a 
medium to low pore space, just as has been exemplified 
in the ideal condition described above. In granular 
soils, the granules, being made up of small particles, 
present much internal pore space. This condition occurs 
only in fine soils, such as loams, silts, and clays, since 
large particles will not cohere firmly enough to produce 
a crumb structure. A fine-textured soil, which will 
puddle more readily than a coarser one, is thus saved 
from a semi-impervious condition by this tendency toward 
granulation. 

The ideal soil condition might be considered to be most 
likely to occur in a loam (Fig. 18). In loamy soil some 
of the particles are large and 
function separately ; others are 
medium in size and tend to form 
the nuclei around which smaller 
particles may cluster to form 
granules, or crumbs. There are 
thus a few large pore spaces 
which facilitate drainage, and 
numberless small openings in 
which water is retained. Air 
therefore finds easy movement 
and sanitation is promoted. In 
such a condition the organic mat- 
ter plays an important part. 
This exists usually as dark, par- 
tially decayed material. It pushes 

apart the grains and lightens the soil, and contributes 
much in bringuig about the loamy condition so favorable 
to plant development. Because of its water-holding 
capacity also it proves a valuable addition. Thus with 




Fig. 18. — The arrange- 
ment of particles in loamy 
soil of good struftural 
condition. (a). Large 
granule; (h), .small sand 
particle ; (c) , large pore 
space ; W), small granules 
with small interstitial 
spaces ; (e) , large sand 
grain. 



112 soils': properties and management 

particles of varying sizes, of a structure partly single- 
grain and partl>' granular, to which has been added by 
natural means sufficient organic matter in an advanced 
stage of decomposition, we have the ideal soil conditions 
for plant development. Yet the same laws govern here 
in a general way as were found to function with homo- 
geneous grains of spherical shape. 

81. The absolute specific gravity of the soil. — The 
structural condition of any soil, be it single-grahi, granular, 
or a favorable combination of the two, has considerable 
influence on certain other physical conditions. One of 
those most affected is the weight. The weight of a soil 
is determined by two factors : the weight of the individ- 
ual particles, or the absolute specific gravity ; and the 
amomit of actual space taken up by such particles in any 
given volume. The latter is really a structural condition 
and is independent to some extent of the size of particles. 
The absolute specific gravity, or weight compared with 
an equal volume of water, of some of the common minerals 
is as follows : — 

Quartz .... 2.7 Apatite . . . 3.2 

Orthoclase . . 2.6 Gypsum . . . 2.8 

Plagioclase . . 2.7 Hematite . . 5.2 

Mica .... 3.0 Limonite . . . 4.0 

Olivine .... 3.1 Serpentine . . 2.6 

Calcite .... 2.7 Chlorite ... 2.2 

Dolomite ... 2.9 Talc .... 2.7 

Although a great range is observed in the absolute 
specific gravities of these common soil-forming minerals, 
it must be . remembered that sucli minerals as quartz 
and feldspar usually make up the bulk of a soil. As a 
consequence it has been found that the absolute specific 



SOME PHYSICAL PROPERTIES OF THE SOIL 113 

gravity of a purely mineral soil varies only between 
narrow limits, these being from 2.6 to 2.8. Nor has 
fineness any appreciable effect, as shown below by Whit- 
ney's ^ determinations on the various separates : — 

Specific Gravity 

Fine gravel (2-1 mm.) 2.647 

Coarse sand (1-.5 mm.) 2.655 

Medium sand (.5-.25 mm.) 2.648 

Fine sand (.25-10 mm.) 2.659 

Very fine sand (.10-05 mm.) .... 2.680 

SiR (.05-.005 mm.) 2.698 

Clay (below .005 mm.) 2.837 

The only marked variation here observed is in the clay 
separate, and this may be due to the concentration of the 
iron-bearing silicates in this grade. However, for all 
practical purposes the average absolute specific gravity 
of a mineral soil may be placed at about 2.70. One 
condition that may vary this is the quantity of organic 
matter present. As the specific gravity of the soil humus 
usually ranges from 1.2 to 1.7, the more humus there is 
present, the lower will be the absolute figure for a given 
soil. A purely organic soil, such as muck or peat, pre- 
sents a variable absolute specific gravity ranging from 
1 .5 to 2.0, according to the amount of wash it has received 
from external sources. Some humus-loam soils may 
drop as low as 2.1. Nevertheless for general calculations 
the average arable soil may be considered to have an 
absolute specific gravity of about 2.70. 

82. Apparent specific gravity. — Since all soils contain 
more or less pore space, depend mg on textural and struc- 

1 Whitney, M. Some Physical Properties of Soils. U. S. 
D. A., Weather Bur., Bui. 4, p. 34. 1892. 
I 



114 SOILS: PROPERTIES AND MANAGEMENT 



(cnmiE 



tural conditions, the actual weight of the absolutely dry 
soil in any volume is of great imi)ortance. This is ex- 
pressed as is the absolute specific gravity of any material, 
the weight of an equal volume of water being used as a 
unit. Because of their tendency to granulate, fine soils 
have a very large amount of pore space, as has been shown 
in the discussion of structure ; it is to be expected, there- 
fore, that they will weigh less in any particular volume 
than will soils made up of large particles. Coarse soils 
are heavy soils, as far as weight is concerned. Mineral 
soils may range in apparent specific gravity^ from 1.10 
to 1.20 for clay to 1.65 to 1.75 for sand. Humous loams 
may drop as low as 1.00, and muck often reaches the 

low figure of .40. The appar- 
ent specific gravity is always 
expressed on the basis of abso- 
lutely dry soil. 

In the field the absolute 
specific gravity of a soil may 
be determined by drivhig a 
cylinder of known volume into 
the ground and obtaining 
thereby a core of natural soil 
(see Fig. 19). By weighing 
the soil and then determining 
the amount of water that it 
holds, the amount of absolutely 
dry soil may be ascertained. 
Dividing this by the weight 
of an equal volume of water 
gives the apparent specific 

1 See Whitne5^ M. Some Phj^sical Properties of Soils. 
U. S. D. A., Weather Bur., Bui. 4. 1892. 



Fig. 19. — Cylinder for deter- 
mining the apparent specific 
gravity of soil in the field. 
The cutting edge at (6) is 
drawn in somewhat to pre- 
vent excessive friction be- 
tween the sides of the cylin- 
der and the entering soil core. 



SOME PHYSICAL PROPERTIES OF THE SOIL 115 

gravity for that soil. A laboratory determination may be 
made by putting the soil into a receptacle of known volimie 
and weighing it. From the weight of the absolutely 
dry soil and the weight of an equal volume of water, the ap- 
parent specific gravity may be calculated. This method 
will give only approximate results, however, as the struc- 
tural relationships are more or less artificial. The only 
reliable method is the one first described. 

83. Actual weight of a soil. — With the apparent 
specific gravity of a soil known, its weight in pounds to 
the cubic foot may be found by multiplying by 62.42. 
Soils may vary in weight from 68 to 80 poimds for clays 
and silts to 100 to 110 pounds for sand. The greater the 
humus content, the less is this weight to the cubic foot. 
A muck soil often weighs as little as 25 or 30 pounds. 
This weight, of course, is for absolutely dry soil and does 
not include the water present, which may be much or 
little, according to circumstances. The actual weight 
of a soil is often expressed in acre-feet. An acre-foot of 
soil refers to a volume of soil one acre in extent and one 
foot deep. In the same way we may have an acre-eight- 
inches or an acre-six-inches. The weight of an acre-foot 
of soil usually varies from 3,500,000 to 4,000,000 poimds ; 
granulation and organic matter ma}- modif}' this con- 
siderably. The value of knowing the actual weight of 
a soil lies in the possibility of calculating thereby the 
amount of water, the amomit of humus, or the actual 
number of pounds of the mineral constituents present in 
the soil. Such information affords a ready means of 
comparmg two soils as to their crop-producing capabilities. 

84. Pore space in soil. — The pore space in soil is 
due largely to structural conditions. As already em- 
phasized, the coarser the soil, the smaller is the aggregate 



116 SOILS: PROPEETIES AND MANAGEMENT 

amount of internal space. Each individual space is 
larger under such conditions, and this accounts for the 
ready movement of water and air through such soils. 
A clay soil, while containing a very large amount of pore 
space, has the disadvantage of very minute individual 
pores. The large amount of space occurs because of 
the lightness of the particles and the tendency toward 
granulation. The small size of the individual spaces 
is a direct function of size of particle, or texture. 

A very simple formula may be used for a determination 
of the percentage of pore space in any soil, provided the 
absolute and the apparent specific gravity is known : — 



Percentage of pore space = 100 — 



Ap. Sp. Gr . 100 
Ab. Sp. Gr. 



00] 



Thus a soil having an apparent specific gravity of 1.60 
and an absolute specific gravity of 2.60 has 38.5 per ceiit 
of pore space ; while in a soil in which the above figures 
are 1.10 and 2.50, respectively, the percentage of pore 
space is 56. The following figures, taken from King,^ 
illustrate the relation that texture holds to total pore 

space m sous : Percentage of 

Pore Space 

Sandy soil 32.49 

Loam 34.49 

Heavy loam 44.15 

Loamy clay soil 45.32 

Clayey loam 47.10 

Clay 48.00 

Very fine clay 52.94 

1 King, F. H. Physics of Agriculture, p. 124. Published 
by the author, Madison, Wisconsin. 1910. 



SOME PHYSICAL PROPERTIES OF THE SOIL 117 

The pore space in any of these soils is, of course, subject 
to considerable fluctuation, especially in the surface 
soil, due to tillage and the mcorporation of organic matter ; 
hence a sandy loam might under certain conditions present 
more pore space than a silt or a clay loam. When soils 
are in the physical condition for the best plant growth, 
however, the rule holds that, the finer the soil, the greater 
is the pore space. The differences in pore space between 
the surface soil and the subsoil in Wisconsin are shown 
by King ^ as follows : — 



First foot 
Second foot 
Third foot 
Fourth foot 
Fifth foot 
Sixth foot 



Weight per 


Percentage of 


Cubic Foot 


Pore Space 


79.0 


52.2 


92.6 


44.0 


104.6 


36.8 


106.2 


35.8 


111.0 


32.9 


111.1 


32.8 



The pore space in a normal soil is occupied by water 
and air. If the water content is low, the air space is 
large, and vice versa. Thus the relationships of the total 
pore space and the size of the individual spaces to the 
amount of air and water contained, to their movement 
through the soil, to soil sanitation, to root extension, to 
bacterial action, and to cropping conditions in general, 
become apparent. It is the regulation of this pore space 
that is really studied in any structural consideration. 
The effect on plant growth of a change in pore space is 
the final test of its advisability. 



^ King, F. H. Physics of Agriculture, p. 111. 
by the author, Madison, Wisconsin. 1910. 



Published 



118 SOILS: PROPERTIES A XT) MANAGEMENT 

85. The number of soil particles. - The number of 
particles in any given volume of soil is really determined 
by texture, and, as this number determines very largely 
the probable arrangement of the soil grains, structure 
becomes in turn dependent on the size of grain. Since 
soil particles run to very small diameters, the number 
in any given volume is very large, especially when we 
are dealing with fine-textured soils or with soils of com- 
pact structural condition. Any calculation of the number 
of particles present in a soil is open to considerable in- 
accuracy, first, because it is impossible to get a correct 
figure for the average diameter of the particles of any 
soil or of the various groups of separates that go to make 
it up, and, secondly, because it must be assumed in the 
calculation that the particles are spherical. This assump- 
tion is of course incorrect, as has already been demon- 
strated ; but it must be entertahied in order to obtain 
approximate ideas as to the number of grains in any soil. 

The number of particles in any soil sample may be 
arrived at from a mechanical analysis and the diameters 
that limit each group. Using the average diameter of 
each group together with the percentage of the groups 
in a given sample, the number of particles may be cal- 
culated by the following formula : — 

Number of particles in a _ Weight of sample in grams 
sample of soil ~ 1/6 n D^ X 2.70 

The formula 1/6 tt D^ is that used for determining the 
volume of a sphere, the diameter hi this case being ex- 
pressed in centimeters. The volume of the sphere, then, 
is obtained in cul)ic centimeters, which must be multiplied 
by the absolute specific gravity of soil minerals, or 2.70, 



SOME PUYSICAL PROPERTIES OF THE SOIL 119 

in order that the weight in grams of a single soil grain 
may be obtained. A calculation by this method of the 
number of particles in a sandy loam is given below : — 



Separates 



Fine grav- 
el . . 

Coarse 
sand . 

Medium 
sand . 

Fine 
sand . 

Very fine 
sand . 

Silt . . 

Clay . . 



Limits 



2-1 mm. 
1-.5 mm. 
.5-. 25 mm. 



.25-. 10 mm. 

.10-.05 mm. 
.05-.005 mm., 
below .005 mm, 



Number op Parti- x<e,'^ '^< 
CLEs to the Gram! g jmS 
OP Each Separate ^ ^ >; ^ 



209 

1,670 

13,410 

131,900 

1,676,500 

35,934,000 

45,632,000,000 



1 

4 

25 

35 

20 

10 

5 



Approximate 

Number of 

Particles in one 

Gram of Sandy 

Loam 



3 

2,281 



2 

67 

3,352 

46. 165 

335,300 
,.593,400 
,600,000 



2,285,578,286 



A very great error is introduced by this method, es- 
pecially in assuming that the average size of particles 
for the clay separate is .0025 millimeter. As the clay 
particles may become molecular complexes and conse- 
quently are very, very small, it stands to reason that 
such an assumption is far from correct. Nevertheless, 
it gives a very good idea as to the immense number of 
grains that we have to deal with, even in the coarsest of 
soils. A few figures as to the approximate number of 
particles in various average soil classes of the United 
States,^ as reported by the Bureau of Soils, are given 
below : — 



For mechanical analysis of the classes, see Chapter VI, p. 104. 



120 SOILS: PROPERTIES AND MANAGEMENT 



Approximate Number of Particles to the Gram in 
Various Classes of Soil in the United States 



Class 



Coarse sands . . 
Sands . . . . 
Fine sands . . 
Sandy loams 
Fine sandy loams 
Loams .... 
Silt loams . 
Sandy clays . 
Clay loams 
Silty clay loams 
Clays .... 



Approximate Number of 
Particles 



2,299 

2,287 

1,826 

5,483 

5,485 

7,332 

6,868 

12,324 

11,877 

11,430 

19,177 



,145,360 
,251,842 
,176,893 
,797,920 
,069,147 
,679,042 
,546,664 
,914,033 
,875,092 
,037,544 
,571,994 



86. Surface exposed by soil particles. — Besides giving 
an actual numerical figure and an insiglit into the prob- 
able structural relationships of a soil, the approximate 
number of particles may serve still another purpose — 
that of enabling us to calculate the aggregate internal 
surface exposed by the soil grains. The surfaces of the 
grains hold more or less water according to their area, 
and they increase the amount of chemical and biological 
activities — functions so necessary to a continuous re- 
placement in the soil solution of the elements withdrawn 
by the plant. The minerals in the soil are all very re- 
sistant to solution ; if they were not, they would long 
ago have been leached away. Such materials, while 
almost insoluble, allow the amount of material going 
into solution to be notably increased by fineness of tex- 
ture, although their solubility remains the same. The 
fineness of the particles, then, presents another significant 
feature besides those already pointed out. 



SOME PHYSICAL PROPERTIES OF THE SOIL 121 

Another important property of the surface of the 
grains is the tendency toward the retention of soluble 
material in a partially or wholly available condition for 
plant use. This power, designated as adsorption, is 
one exhibited to a high degree by fine soils, in which 
the individual pore spaces are small and the amount of 
surface exposed is large. It is an important factor to 
be observed in the addition to the soil of soluble fertilizing 
constituents. Adsorption may also, by bringing materials 
into closer contact, hasten or retard certain chemical 
actions. Reactions may thus be expected to go on in the 
soil that would not take place in the laboratory beaker. 
The relation of this adsorption to bacterial activity also 
cannot be overlooked. 

The aggregate area presented by soil particles is very 
large, even for the coarser soils. With the finer soils, 
because of the immense number of particles, a figure is 
reached that is almost beyond comprehension. When 
the approximate number of particles and their sizes 
in any given weight of soil are known, the internal surface 
may be calculated by the following formula : — 

Surface = tt D^ X number of particles 

As the estimation of the number of particles in a soil is 
so inaccurate, it is evident that a calculation of the 
surface exposed based on such a figure must be more in 
error. 

However, to give some idea of the internal surface ex- 
posed by ordinary soils, the calculations made on a few of 
the average soil classes of the United States, already 
presented,^ are given in the table on the following page. 

1 See Chapter VI, p. 104. 



122 SOILS: PROPERTIES AND MANAGEMENT 



Approximate Internal Area exposed by Average Classes 
OF United States Soils 





Square Inches 
PER Gram 


Square Feet 
PER Pound 


.\CRES PER 

Acre-foot of 
3,500,000 Pounds 


Coarse sands . 
Sands . . . 
Fine sands 
Sandy loams . 
Fine sandy loami? 
Loams . 
Silt loams . . 
Sandy clays 
C^lay loams 
Silty clay loams 
Clays . . . 






91 
89 

79 
213 
222 
294 
307 
417 
430 
458 
653 


286 

280 

248 

671 

699 

926 

967 

1313 

1354 

1442 

2057 


23,055 

22,549 

20,014 

53,965 

56,180 

74,410 

77,700 

105,540 

108,830 

115,910 

165,270 



It is at once apparent that the amount of surface 
exposed by the soil grains of even a sand is tremendous. 
It is not to be wondered at that the slowly soluble minerals 
are able to supply sufficient food to the crop growing on 
the soil, when such a large amount of surface is contmually 
available for chemical action. The figures presented for 
an acre-foot of soil are almost too large for adequate com- 
prehension. It is quite evident that the finer the soil, 
the greater is the amount of internal surface. For ex- 
ample, a sandy loam weighing 90 pounds to the cubic 
foot would present 00,390 square feet of surface, while 
a clay weighing 75 pounds to the cubic foot would expose 
about 154,275 square feet. This is equivalent to 1.39 
and )^j.54 acres, respectively. 

87. The effective mean diameter of soil particles. — 
It is very evident that the calculations presented above, 
both as to the number of particles and as to the hiternal 



SOME PHYSICAL PROPERTIES OF THE SOIL 123 

surface exposed, are far from correct, as we can arrive 
at no definite figure as to the average size of grain. Neither 
do we know the actual structural conditions. In con- 
sidering these inaccuracies King ^ decided that we were 
in need of a single term which not only would give an 
indication regarding the size of grain, but also would 
carry with it definite ideas as to the arrangement of the 
particles, particularly as to the rate at which they would 
allow air and water to pass through. This would bring 
the considerations nearer to the plant, as permeability 
very largely determines the conditions for plant develop- 
ment. King, while he could obtain neither the mean 
diameter of particle nor the actual internal surface, found 
that he could determine with considerable accuracy, 
particularly in sands, the diameter of grain which if sub- 
stituted for the actual one would permit under like con- 
ditions the same rate of air and water movement. This 
size of grain he designated as the effective mean diameter 
of particle for that particular soil. 

The theory of the method is presented by Schlicter,^ 
and is based on the flow of fluids through capillary tubes. 
From the observed rate of the flow of air through a soil 
column under controlled conditions, it is possible to 
calculate the effective diameter of the interstitial spaces. 
From these data the size of the spherical grains which 
would be necessary to form such pore spaces, or capillary 
tubes, is computed by appropriate formulae. Such a 
figure represents the effective mean diameter of the soil, 



1 King, F. H. Physics of Agriculture, pp. 119-120. Pub- 
lished by the author, Madison, Wisconsin. 1910. 

' Schlicter, C. S. Theoretical Investigation of the Move- 
ment of Ground Waters. U. S. Geol. Survey, 19th Ann. Rept., 
Part II, pp. 301-384. 1899. 



124 SOILS: PROPERTIES AND MANAGEMENT 




' . /'^ ri^' 



^ \ 



from which the effective surface exposed can be deter- 
mined. Thus, desif!;natinf]; a soil as having an effective 
mean diameter of particle of .()().52 millimeter merely 
indicates that this particular soil shows an air and 
water movement the same as would be shown by a 
homogeneous soil with spherical particles of that diameter. 

The apparatus ^ for the de- 
termination consists of a cylin- 
der in which is placed a sample 
/^::::\ ^'-—^ of air-dry soil, the pore space 

^' l)eing carefully determined by 

weighing. The rate of air 
movement is then determined 
by connecting with an aspi- 
rator, the temperature and 
the pressure being constantly 
under control. The reading is 
usually calculated to a tem- 
l)erature of 20° C. The fact 
that the structural condition 
of the soil is likeh" to be dis- 
turbed in placing the sample 
in the aspirator tube detracts 
from the accuracy, especially 
in fine soils. Nevertheless, 

Fig 20. - Kings aspirator for J^J, , Jo^u^^l \-^[^ results fairlv 
the determination of the rate , , , , ' 

of air movement through accurate, and showed that 
soils. (G) Pressure gauge; ^hc calculated and the ob- 

(S), soil column ; (L), water; ^ n e i i 

(.4), aspirator; (IT), weight, served tlow ot Water through 



rf 



fl 



1 King, F. H. Principles and Conditions of the Movements 

of (Jround Water. U. S. Geol. Survey, 19th Ann. Kept., Part 

II, pp. 222-224. 1899. A complete discussion is given of 
King's ideas in this article, pp. 67-294. 



SOME PHYSICAL PROPERTIES OF THE SOIL 125 



sands ^ agreed rather closely (see Fig. 20). The effective 
diameter of the particles of some of our common soils, to- 
gether with the effective surface exposed, is given 
below : - -^ 



Soil 


Effective 
Diameter 


Percextage 

OF Pore 

Space 


Effective Sur- 
face Exposed in 
One Cubic Foot 
OP Soil 


Coarse sandy soil 
Sandy soil . 
Sandy loam . . 
Loam .... 
Loamy clay soil . 
Fine clay soil . . 
Very fine clay 




.1432 mm. 
.0755 mm. 
.0303 mm. 
.0219 mm. 
.0140 mm. 
.008(5 mm. 
.0049 mm. 


34.9 
34.4 
38.8 
44.1 
45.3 
48.0 
52.9 


8,318 sq. ft. 

15,870 sq. ft. 

36,880 sq. ft. 

46,510. sq. ft. 

71,316 sq. ft. 
110,500 sq. ft. 
173,700 sq. ft. 



The method of King has certain ad\'antages, besides 
giving an idea as to the number of particles, their internal 
surface, and the relation of this internal surface to soil 
conditions. In the first place, a single figure is used 
to express the size of particle ; secondly, from this effec- 
tive size of particle the probable rate of air and water 
movement may be calculated ; and, thirdly, the number 
of particles and the internal surface calculated therefrom 
have a fairly definite relationship to the plant, as such 
figures are so closely correlated to the circulation of air 
and water. 

' King, F. H. Physics of Agriculture, p. 123. Published 
bv the author, Madison, Wisconsin. 1910. 
' ^Ibid., p. 124. 



CHAPTER VIII 
THE ORGANIC MATTER OF THE SOIL 

One of the essential differences between a soil and a 
mass of rock fragments lies in the organic content of the 
former. Organic matter is a necessary constituent in 
order that finely ground mineral material may be desig- 
nated as a soil and that it may grow crops successfully. 
Physical condition depends largely on the presence, 
and chemical reaction is greatly accelerated by the de- 
cay, of organic matter. In the process of soil formation 
its addition is more or less a secondary step. In residual 
debris the amount of organic matter held by the growing 
soil increases as the process of weathering goes on ; in 
glacial soils, howe\er, the matrix, or skeleton of the soil, 
is already formed before there is an opportunity for humus 
to become incorporated therein. The final result from 
the mixing of the minerals carrying numerous weathered 
and altered products with the decayed or partialh' de- 
cayed organic matter that is sure to accumulate, must 
be a mass much more complicated than either of the 
original constituents. It is hardly necessary to further 
emphasize the complexity of the average soil, the reasons 
tluTcfor, and the difficulties in studying the question. 

88. The source and distribution of organic matter. — 
The source of practically all soil organic matter is plant 
tissue. Some of this matter accumulates from the above- 
ground parts of i^lants that have died and fallen down 

120 



THE ORGANIC MATTER OF THE SOIL 



127 



to become niLxed with the surface soil ; the remainder 
is a result of root extension and subsequent decay. The 
organic matter of the surface soil is derived from the 
tops and the roots of plants growing on it, while that of 
the subsoil is very largely a result of root extension and 
subsequent decomposition. The relationship between the 
humus content of three soils and the roots developed is 
shown by the following data presented by Kostytscheff ^ 
and quoted by Hilgard - and Wollny ^ : — 

Root Content and Percentage of Humus in Three 
Russian Soils 





1 


2 


3 


Depth 

(inches) 


Roots 


Humus 


Roots 


Humus 


Roots 


Humus 


6 
12 
18 
24 
30 
36 
42 
48 
54 


100 
89 
67 
47 
47 
35 
24 
14 
7 


5.4 
4.8 
3.6 
2.5 
2.5 
1.8 
1.3 
.8 
.3 


100 
64 
48 
35 
26 
18 
6 


8.1 
5.2 
3.9 
2.8 
2.1 
1.5 
.5 


100 
80 
70 

58 
38 
33 
16 


9.6 

7.7 
6.7 
5.6 
3.6 
3.1 
1.5 



89. Composition of plants. — It is usual, in classifying 
the materials composing plant tissue, to group them under 
three heads — carbohydrates, fats and oils, and proteins. 



1 Kostytscheff, M. P. Les Terres Noires de Russie. Annales 
de la Sci. Agron., Tome II, pp. 165-191. 1887. 

- Hilgard, E. W. Soils, p. 130. New York. 1906. 

' Wollny, E. Die Zersetzung der Organischen Stoffe, p. 194. 
Heidelberg. 1897. 



128 SOILS: PROPERTIES AX I) MANAGEMENT 

The carbohydrates, havino; the general formula of 
Cx(HoO)n, inchide such compounds as ghicose, starch, 
celhdose, dextrose, cane sugar, and the Uke. The fats 
and oils may be represented in plants by such glycerides 
as butyrin, stearin, olein, palmitin, and the like. The 
proteins are by far the most comjjlicated of the three 
principal compounds, as they may carry not only carbon, 
hydrogen, oxygen, and nitrogen, but also mineral elements 
such as sulfur, phosphorus, lime, iron, and other elements. 
They are compounds of high molecular weight and are 
mostly of unknown constitution. Simple proteins, such 
as albumin, globulin, protamins, and others, are found 
in plants, besides certain derived proteins such as 
proteosis and peptones. In addition to all these, there 
is a host of other compounds that have no small influence 
on the composition of the soil organic matter. Among 
these are the alkaloids, waxes, tannins, phenols and their 
derivatives, hydrocarbons, resins, acids, aldehydes, and 
others. 

The original plant tissue, therefore, while fairly well 
known, as to chemical constitution, is far from simple. 
The degradation of such material, especially in the i)res- 
ence of complex mineral products, will evidently give rise 
at first to compounds no simpler ; in fact, the chances 
are that the resulting compounds will be much more com- 
plicated. It is only later in the processes of decay that 
simple products result. 

90. Decay of organic matter in -soils. — From the fact 
that weathering in general is a process of simplification, 
and since it is evident that the plant tissue as it enters 
the soil is so very complex, the general change that the 
organic matter undergoes must be one of simj)lification. 
This simplification, however, is very slow, and many of 



THE ORGANIC MATTER OF THE SOIL 129 

the prochicts Iniilt up are more complex than the original 
tissue. Most of this decay and simplification is due to 
that great group of organisms so universally present in 
soil, called bacteria. Some of these are putrefactive in 
their action, while others deal to a large extent with the 
products of the decomposition. All, however, exert a 
general simplifying influence. The action of such or- 
ganisms may be direct, but is more likely to be enzymotic 
in its nature, and may take place either within or outside 
of the cell. A cycle is therefore set up, in which the higher 
plants and animals are occupied in building up, while 
bacteria are tearing down and reducing the residue of 
plant action to simple forms, such as can be ultimately 
utilized again in plant nutrition. The great importance 
of bacteria is thus evident, and the encouragement of 
their growth and function is clearly a part of good soil 
management. 

When the complex molecules that make up plant 
tissue break dow^n, they split along definite hues of cleav- 
age, depending on the structure of the original molecule. 
These bodies, which are usually simpler in nature than 
those from which they have sprung, are called cleavage 
products, and without a doubt they are the primary 
products of the first step in organic decay. These com- 
pounds are subject to still further change, and because 
of the great number of agencies at work the secondary 
products that result may be simpler or more complex, 
according to conditions. Bacteria have a tendency, 
while tearing down organic matter, to construct certain 
built-up products which present a very complicated 
molecide until they are in turn degraded. The secondary 
products therefore vary widely because of differences in 
temperature, moisture, aeration, and other conditions. 

K 



130 SOILS: PROPERTIES AND MANAGEMENT 

The character of the secondary products probably ex- 
hibits a greater variation than does that of the original 
plant tissue. In the process of decay these products 
become black or brown in color, and are usually designated 
as humous materials in the soil. Organic matter, then, 
covers all the material of organic origin hi the soil, and 
may refer not only to the original plant tissue, but also 
to that which has lost its identity in the secondary prod- 
ucts. Humus refers specifically to the prmiary and the 
secondary products of decay, and may be simple or com- 
plex, according to conditions. 

As the process of decay goes on, certain end products 
result. These are partially solid and partially gaseous. 
Carbon dioxide is a universal product of bacterial activity 
of all kinds, as is also water. Besides these, urea, am- 
monia, nitrites, and nitrates may result from nitrogenous 
decay. The three general classes of organic matter found 
in soil may be illustrated by the following diagram : — 

PLANT TISSUE I HUMUS I END PRODUCTS 

UNDECOMPOSED MATTER | SECONDARY AND INTERMEDIATE | SIMPLE MATERIAL 

Fig. 21. — Diagram illustrating the three general classes of organic 
matter found in soils. 

It is therefore possible to have present, besides the 
original organic constituents which are mostly of plant 
origin, not only their primary and secondary degradation 
products, but also compounds either torn down or built 
up from these. An attempt to enumerate even the 
original compounds in the plant tissue, or even the simple 
end products of complete decay, would result in a long 
list of materials representing almost every known class 
of organic compound. Such a procedure is possible, 
but is unnecessary as the important ones have already 



THE ORGANIC MATTER OF THE SOIL 131 

been mentioiiefl. It is to hv kept in mind that the simpler 
products of decay are the ones utihze(l by crops, although 
it is a well-established fact that some of the secondary 
and intermediate compounds may be taken up by certain 
plants and probably are of some importance from the 
standpoint of use as plant-food. 

91. Composition of the soil humus. — It is evident 
that the most complicated parts of the organic matter 
in the soil are the primary and the secondary products 
of decay, or the so-called soil humus. The study of this 
matter is difficult and calls for the very highest knowledge 
of organic chemistry. This is true for two reasons : 
first, because of the complexity of these compounds; 
and, secondly, because they are continually changing. 
A certain compound present in the soil one week may 
disappear the next week. Moreover, while some of the 
soil humus is soluble in water and may circulate in the 
soil solution, the bulk of it is insoluble. This in itself 
presents difficulties. When the soil humus is treated 
with the various extractive agents, reactions may be 
induced which would not take place in a normal soil. 
Compounds are then formed which not only would be 
abnormal, but would probably not exist imder natural 
conditions. 

A great many chemists have worked on the problem of 
the constitution of the organic matter of the soil and 
have published their results. The ideas of the early 
workers are really embodied in the conclusions advanced 
by ]\Iulder,^ who w^as in many ways far in advance of his 

1 Mulder, T. J. Die Organisehen Bestandtheile im Boden. 
Chemie der Aekerkrume, I, pp. 308-360. Berlin, 1863. Also, 
Wiley, H. W. Agricultural Analysis, Vol. 1, p. 53. Easton, 
Pa. 1906. 



132 SOILS: PROPERTIES AND MANAGEMENT 

time. Mulder contended that the organic matter con- 
sisted of seven distinct compomids, as foHows : — 

1 and 2. Ulmic acid and uhiiin 5. Geic acid 
3 and 4. Hmnic acid and humin 6. Apocrenic acid 
7. Crenic acid 

These bodies he considered as arising from one another 
by oxidation ; thus, ulmic acid (C40H14O12) gave humic 
acid (C40H12O12), which in turn yielded geic acid 
(C40H12O14), followed by apocrenic acid (C48H12O24), 
and finally by crenic acid (C24H12O16). Such a classi- 
fication seems very simple, but certain flaws are at once 
noticeable. In the first place, nitrogen does not find a 
place in any of these formuhe ; secondly, the compounds 
are simpler than most plant tissue, which is not what 
would be expected, especially with some of the degrada- 
tion compounds ; thirdly, none of these products ha^•e 
united with the bases in the soil, a reaction that would 
be very likely to take place especially with acid compounds. 
Even the investigators ^ of iNIulder's time obtained dis- 
cordant results, but these were explained for the time 
being by assuming that the discrepancies occurred because 
of added molecules of water. 

Later investigators, while progresshig only slightly 
toward definite results, did accomplish one thing of im- 
portance, and that was throwing considerable doubt 
on the old ideas of the Mulder school of chemists. This 
again opened up the question as to the composition of 
the soil organic matter, especially the humous constituents. 
Thus, while it is evident that no such compounds as geic 

1 See Sehrciner, ()., and Shorey, E. C. The Isolation of 
Harmful Organic Substances from Soils. U. S. D. A., Bur. 
Soils, Bui. .53, pp. 1.5-lG. 1909. 



THE ORGANIC MATTER OF THE SOIL 133 

acid, humic acid, or crenic acid exist in the soil, one name 
has persisted in soil literature — that of humus and 
humic acid. The word humus, as already indicated, 
does not relate to any definite compound, but to the 
great mass of primary and secondary' products of bio- 
logical and chemical organic decay taking place in the 
soil. One of the men whose work established beyond 
a doubt the fact that humus was not a definite compound 
was Van Bemmelen.^ His investigations still further 
showed that the soil humus was largely in a colloidal 
condition, and therefore exhibited properties quite dis- 
tinct from those shown by crystalloids. 

In recent years investigation has again been directed 
toward the immense field opened by the overthrow of 
the jNIulderian school. Baumann,^ by his researches, 
has shown freshly precipitated humus to possess properties 
which are largely colloidal in nature. Among these char- 
acteristics are high water capacity, great adsorptive power 
for certain salts, ready mixture with other colloids, power 
to decompose salts, great shrinkage on drying, and coagula- 
tion in the presence of electrolytes. Jodidi ^ has studied 
the composition of the acid-soluble organic nitrogen in 
peat and in mineral soils. The nitrogenous compomids 
thus obtained can be divided into the following 
groups : — 

1 Van Bemmelen, J. M. Die Absorptions Verbindungen 
und das Absorptionsvermogen der Aekererde. Landw. Ver- 
suehs. Stat., Band 35, Seite 67-136. 1888. 

"^ Baumann, A. Untersuchungen liber die Humussauren. 
Mitt. d. K. bajT. Moorkulturanstalt, Heft 3, Seite .53-123. 
1909. 

' Jodidi, S. L. Organic Nitrogenous Compounds in Peat 
Soils I. Mich. Agri. Exp. Sta., Tech. Bui. 4, November, 1909. 
Also, The Chemical Nature of the Organic Nitrogen in Soil. 
Iowa Agr. Exp. Sta., Research Bui. I, June, 1911. 



134 soils: properties and management 

1. Nitric iiitrogeii 3. Diamiiio acids 

2. Ammoniacal nitrogen 4. Acid amides 

5. Monamino acids 

The two latter constituents were found to make up the 
bulk of the organic nitrogen, but quantitative determina- 
tions proved uncertain. These compounds produced 
ammonia readily, the rate depending on their chemical 
structure. 

92. The work of Oswald Schreiner. — Of the chemists 
who have been most active and most successful, Schreiner ' 
deserves especial mention. Our present knowledge of the 
chemical constitution of the organic matter of the soil is 
very largely due to his eft'orts. While he realized that 
the isolation of specific compounds from the soil was likely 
to present insurmountable problems, and that the iden- 
tification of such compoiuids after they were obtained 
might be very difficult, he undertook a systematic ex- 
traction of the soil. As a result of several years of work 
he was able to isolate and identify a number of com- 
pounds. The complexity and varied character of these 
compounds is revealed by the following list of the more 
important bodies isolated : — 

List of Compounds isolated from Soil Organic 
jNIatter by Schreiner, Siiorey, Skinner, Reed, 
and others, of the u. s. bureau of soils 

Hentriacontane, C31H64 Picoline carboxylic acid, 

Dihydroxy stearic acid, C7H7O2N 

C18H36O4 Ilistidine, CeHgOoXs 

'Schreiner, ()., atul Shorey, E. C. The Isolation of Harm- 
ful Organic Substances from Soils. U. S. D. A., Bur. Soils, 
Bui. 53, 1909 ; also, Buls. 47, 70, 74, 77, 80, 83, 87, 88, and 90. 



THE ORGANIC MATTER OF THE SOIL 



135 



Monohydroxystearic acid, 

CigHaeOs 
Agroceric acid, C21H42O3 
Agrosteral, C22H22O . HoO 
Paraffinic acid, r24H4802 
Lignoceric acid, C24H48O2 
Phytosterol, C26H44O . HoO 
Pentosan, C5H8O4 
Oxalic acid, C2H2O4 
Succinic acid, C4H6O4 
Sacharaic acid, CeHgOio 
Acrylic acid, C3H4O2 
Mannite, CeHuOe 
Rhamnose, C6Hi40io 
Salicylic aldehyde, 

C6H4OHCOH 



Arginine, C6H14O2X4 
Cytosine, C4H5OX3 . H2O 
Xanthine, C5H4O2X4 
Hypoxanthine, €51140X^4 
Tysine, C6Hi402X'2 
Adenine, C5H5X5 
Choline, C5H15O2X 
Trimethylamine, C3H9N 
Quanine, CHsX's 
Creatinine, C4H7ON3 
Creatine, C4H902X'3 
X'^ucleic acid (constitution 

unknown) 
Trithiobenzaldehyde, 

(C6H5CSH)3 



From a chemical standpoint these compounds may be 
classified under four heads : (1) those containing carbon 
and hydrogen; (2) those containing carbon, hydrogen, 
and oxygen ; (3) those containing carbon, hydrogen, and 
nitrogen, or carbon, hydrogen, oxygen, and nitrogen ; 
(4) those containing sulfur in combination with the 
elements listed above. With the possible presence in 
soils of compounds containing five elements, it is of 
little wonder that the subject is a complicated one. It 
is evident, moreover, that the list given above is only a 
partial one, and many other compounds of an even more 
intricate composition will later be isolated. 

So far as the plant is concerned, the compounds may 
be divided into three groups — those that are beneficial, 
those that are neutral, and those that are toxic, or harm- 
ful, hi their effects. As an example of the first group, 



136 SOILS: PROPERTIES AND MANAGEMENT 

histidine and creatinine ^ may be mentioned. Here is 
a case in which the compounds found in the soil humus 
may exert a stimulating effect on plant growth, and 
may also be a source of plant-food, supplementing the 
nitrates ^ to a certain extent. That the nitrogen of the 
soil organic matter may be utilized by plants is well sum- 
marized by the publications of Hutchinson and ]\Iiller.^ 
As an example of a harmful compound arising from the 
decomposition of the organic matter, dihydroxystearic 
acid^ may be mentioned as one of the best known. This 
compound was the first to be isolated and identified by 
Schreiner, and is very toxic. 

93. Toxic material in the soil. — The discovery of 
such compounds in the soil has revived the old theor\' 
of toxicity,"* by which the infertility of certain soils is 
accounted for. Root excretions are also held to be 
detrimental to succeeding crops of the same kind. The 

1 Sldnner, J. J. Effect of Histidine and Arginine as Soil 
Constituents. Eighth Internat. Cong. App. Chem., Vol. XV, 
pp. 2.53-264. 1912. Also, Beneficial Effects of Creatinine 
and Creatine on Growth. Bot. Gaz., Vol. 54, No. 2, pp. 1.52- 
163. 1912. 

^ Schreiner, 0., and Skinner, J. J. Nitrogenous Soil Con- 
stituents and Their Bearing upon Soil Fertility. U. S. D. A., 
Bur. Soils, Bui. '87, p. 68. 1912. Also, Schreiner, O., and others. 
A Beneficial Organic Constituent of Soils i Creatinine. U. S. 
D. A., Bur. Soils, Bui. 83, p. 44. 1911. 

•■' Hutchinson, H. B., and Miller, N. H. J. The Direct 
Assimilation of Inorganic and Organic Forms of Nitrogen by 
Higher Plants. Jour. Agr. Sei., Vol. 4, Part 3, pp. 282-302. 
1912. 

'' Schreiner, O., and Skinner, J. J. Some Effects of a Harm- 
ful Organic Soil Constituent. U. S. D. A., Bur. Soils, Bui. 70. 
1910. 

* See Schreiner, O., and Reed, H. S. Some Factors Influ- 
encing Soil Fertility. U. S. D. A., Bur. Soils, Bui. 40, pp. 36- 
40. 1907. 



THE ORGANIC MATTER OF THE SOIL 137 

toxic materials of tiie soil humus largely originate under 
conditions of poor drainage and aeration, and conse- 
quently are biological in their genesis. The toxicity of 
such compounds as dihydroxystearic acid, picoline car- 
boxylic acid,^ and aldehydes ^ may therefore be overcome 
by oxidation,^ so that good soil aeration is a factor in 
dealing with such conditions. Insufficient sanitation 
of the soil seems to account very largely for the presence 
of soil toxines. Fertilizers, according to Schreiner and 
Skinner/ seem to decrease the harmful effects of such 
compounds ; nitrogenous fertilizers overcoming some 
toxic materials, and phosphorus or potash neutralizing 
others. For example, in water solution and sand culture, 
nitrogen seems especially efficacious in correcting such 
toxic substances as dihydroxystearic acid and vanillin, 
phosphorus is particularly powerful in counteracting 
cumarine, and potash has considerable influence on 
quinone. 

While the real importance of the toxic material generated 
in the soil cannot be fully discussed at this point, it is 
quite evident that such constituents do tend to develop 
under insanitary conditions and must be considered in 

1 Schreiner, 0., and Skinner, J. J. The Isolation of Harm- 
ful Organic vSubstanees from Soils. U. S. D. A., Bur. Soils, 
Bui. 5:3, pp. 4G-49. 1909. 

^ Schreiner, 0., and Skinner, J. J. Harmful Effects of 
Aldehydes in Soils. U. S. D. A., Bui. 108 (Professional Paper). 
1914. 

^ Schreiner, O., and others. Certain Organic Constituents 
of Soils in Relation to Soil Fertihty. U. S. D. A., Bur. Soils, 
Bui. 47, p. .52. 1907. Also, Schreiner, O., and Reed, H. S. 
The Role of Oxidation in Soil Fertihty. U. S. D. A., Bur. 
Soils, Bui. 56, p. 52. 1906. 

* Schreiner, O., and Skinner, J. J. Organic Compounds and 
FertiUzer Action. U. S. D. A., Bur. Soils, Bui. 77. 1911. 



138 SOILS: PROPERTIES AND MANAGEMENT 

the discussion of the composition of that great group of 
intermediate compounds, called humus, arising from the 
decay of the organic matter of the soil. While Schreiner 
found twenty soils, out of a group of sixty taken in eleven 
States of this country, to contain dihydroxystearic acid, 
this does not necessarily mean that this compound in 
itself is a serious detrimental factor. It is very likely 
that such compounds are merely products of improper 
soil conditions, and are to be considered as concomitant 
with depressed crop yields. When such conditions are 
righted, the so-called toxic matter will disappear. Good 
drainage, lime, tillage, a balanced food ration, ])romoted 
aeration and oxidation, are so efficacious in this regard 
that permanent soil toxicity need never be feared by the 
farmer. 

94. End products of humus decay. — As the processes 
of chemical and biological decay of the soil organic matter 
proceed, the simple compounds already noted l)egin to 
appear. This change is of course coordinate with a 
certain amount of synthetic action, but compounds thus 
built up must ultimately succumb to the agencies at 
work and suffer a splitting-up and reduction to simple 
bodies. Carbon dioxide is one of the most important of 
these compounds, being always a product of bacterial 
activity. Its importance has already been noted in the 
discussion of weathering. Here it heightens the sohent 
power of water and tends to increase the amount of plant- 
food carried in the soil solution. Carbonation is a direct 
result of its presence. Carbon dioxide may also tend to 
flocculate colloidal matter in soils, and thus benefit the 
physical conditions. With increased organic matter in 
any soil, tliere greater bacterial action and an increase 
in the carbon dioxide evolved may well be expected. In 



THE ORGANIC MATTER OF THE SOIL 



139 



fact, the carbon dioxide production of a soil is considered 
by some authors ^ to be a measure of bacterial activity. 
With this increase in carbon dioxide the soil air becomes 
more heavily charged and an alteration in bacterial and 
])lant relationships may thereby be induced. The fol- 
lowing figures, by Wollny,^ show the composition of the 
soil atmosphere and the effects of additional humous 
material on the carbon dioxide content : — 



Percentage by 
Volume of 



Soil air (average of 19 analyses) 

Atmospheric air 

A sandy soil 

A sandy soil plus manure . . 




18.33 
20.96 
19.72 
10.35 



While carbon dioxide may be evolved by the splitting-up 
of both carbohydrate and nitrogenous bodies, ammonia 
results only from the latter. It is really the first ex- 
tremely simple nitrogenous body produced. It can be 
utilized by some plants as a source of nitrogen, as is also 
true with certain simple humic bodies, but ordinarily 
it must undergo oxidation. This oxidation results in 
nitrites (NO2) and ultimately in nitrates (NO3), the 
latter being usually considered as the chief source of 
the nitrogen utilized by plants. 

1 Stoklasa, J., and Ernest, A. Ueber den Ursprung, die 
Menge, und die Bedeutung des Kohlendioxyds im Boden. 
Centrlb. Bakt., II, 14, Seite 723-736. 1905. 

- WoUny, E. Die Zersetzung der Organischen Stoffe, 
Seite 2. Heidelberg, 1897. 



140 SOILS: PROPERTIIJS AND MANAGEMENT 

Other end products, such as methane (CH4), hydrogen 
disulfide (HgS), free nitrogen (N), sulfur dioxide (SO2), 
carbon disulfide (CS2), and the like, may also result. 
They are relatively unimportant, however, as regards 
the plant, in comparison to the role played by carbon 
dioxide, ammonia, the nitrites, and the nitrates. The 
production of the nitrates from ammonia particularly 
is very clearly correlated with good soil conditions, es- 
pecially optimum moisture and adequate aeration. The 
proper handling of the soil, then, not only will tend to 
eliminate toxic matter and prevent its further formation, 
but will encourage the proper decay of the soil humus and 
the })r()duction of end products which will function directly 
or indirectly as plant foods. 

Snyder ^ found that when humus was extracted with an 
alkali and then precipitated with an acid, it yielded from 
five to twenty-five per cent of a reddish brown ash. This 
ash contained silica, iron, and alumina, as well as mag- 
nesia, potash, phosphorus, sulfur, sodium, and calcium. 
While part of these mineral constituents may be chemically 
combined with humus, it is probable that some may be 
present because of the adsorptive ca})acity of the organic 
colloids which are always present in humus generated 
under normal conditions. Snyder has estimated that 
in an ordinary soil containing a fair amount of organic 
matter, one-sixth of the phosphorus and one-twelfth of 
the potash may be present in such a state. They are 
then fairly available, and are yielded much more readily 
to the plant than if of a strictly inorganic nature. 

95. Carbonized materials of soil. — After the extrac- 
tion of the soil for the study of the ordinary humus com- 

^ Snyder, Harrv. Production of Humus from Manures. 
Minnesota Agr. Exp. Sta., Bui. 53, pp. 20-30. 1897. 



THE ORGANIC MATTER OF THE SOIL 141 

pounds, a considerable mass of material remains, which 
is insoluble in water, alkali, and other ordinary solvents. 
By the extraction of a large amount of soil, Schreiner ^ 
was able to study this material. He found it susceptible 
to division into six groups, as follows: (1) plant tissue, 
(2) insect and other organized material, (3) charcoal 
particles, (4) lignite, (5) coal particles, and (6) materials 
resembling natural hydrocarbons, as bitumen, asphalt, and 
the like. Such material was found not only near the sur- 
face of the soil, but at depths of jBfteen or twenty feet be- 
low. All the groups above listed were found by Schreiner 
to be represented in the thirty-four soils collected from 
all parts of the United States and subjected to rigid test. 

The exact origin of such material is problematical. 
Forest and prairie fires, infiltration, mild oxidation, and 
lignification might be mentioned. Of a certainty, the 
agencies of distribution are the natural forces engaged 
in physical weathering. This carbonized material is 
important, as it makes up no inconsiderable part of the 
soil humus. It is very resistant, and consequently lends 
stability to the soil organic matter. It can be divided 
into two general groups, organized and unorganized; 
in the former the original structure remains intact, while 
in the latter the original features have been obliterated. 
The study of such material and the changes that it under- 
goes not only increases the list of known organic com- 
pounds existing in the soil, but throws considerable light 
on the nature of the soil organic matter as a whole. 

96. The estimation of the soil organic matter. — 
Many methods have ])een proposed for the determination 

• Schreiner, 0., and Brown, B. E. Occurrence and Nature 
of Carbonized Material in Soils. U. S. D. A., Bur. Soils, 
Bui. 90. 1912. 



142 SOILS: PROPERTIES AND MANAGEMENT 

of the organic matter in soils, but none have proved 
entirely satisfactory, since the composition of this ma- 
terial is so complicated and so likely to change while 
under investigation. Other soil constituents also tend 
to interfere with the determination. Two general methods 
seem w'orthy of mention, as they have been used very 
widel\' in soil analyses and at least give comparative, if 
not absolutely accurate, results. 

Loss on ignition.^ — This is a simple method which 
designs to burn off the organic matter and determine 
its loss by difference. Five grams of dry soil are 
placed in a platinum dish and ignited at a low red 
heat until the organic matter is all oxidized. The 
cold mass is moistened with ammonium carbonate 
and heated to a temperature of 150° C. in order to 
expel the excess of ammonia. The loss is rated as or- 
ganic matter. 

This method is open to the objection that, besides the 
loss of organic matter, a certain small amount of water 
of combination, together with all ammoniacal compounds, 
nitrates, all carbon dioxide, and some alkali chlorides if 
the temperature is carried too high, is driven off. The 
method therefore gives high results, especially in the 
presence of large amounts of hydrated silicates. An 
attempt to replace the carbon dioxide is made in the 
treatment of the cold mass with ammonium carbonate. 
Notwithstanding these objections, this method is one of 
the best and is very generally used all over the world 
in estimating the organic matter of the soil. Very often 

1 Houston, H. A., and McBride, F. W. A Modification of 
Grandeau's Method for the Determination of Humus. U. S. 
D. A., Div. Chem., Bui. 38 (edited by H. W. Wiley), pp. 84-92. 
1893. 



THE ORGANIC MATTER OF THE SOIL 143 

the combustion is carried on in a current of oxygen over 
hot copper oxide. The organic carbon may thus be 
determined very accurately, and the organic matter 
calculated by multiplying the carbon found by the factor 
1.724. 

Chromic acid method} — This method, proposed by 
Wolfl', has been modified and improved by various chem- 
ists. Warington and Peake^ have perhaps done more 
with the method than any other investigators. In the 
United States the modification of Cameron and Brea- 
zeale ^ has been very generally accepted. It consists 
in the treatment of the soil sample with sulfuric acid 
and chromic acid or potassium bichromate. The organic 
matter, in the presence of the sulfuric acid and an oxidizing 
agent, evolves carbon dioxide until, if the mixture is 
boiled, practically all of the carbon is thus driven off. 
This gas is drawn through a train of absorption bulbs, 
caught in a solution of potassium hydrate, and thus 
weighed. On the supposition that organic matter is 
58 per cent carbon, it is very easy to make the calcula- 
tion. The carbon found may be multiplied by 1.724, 
or the carbon dioxide by .471. The product is considered 
as soil organic matter. The results thus obtained are 
usually lower than with combustion or ignition methods, 

1 For comparison of methods, see Wiley, H. W. Principles 
and Practices of Agricultural Analysis, Vol. I, pp. 347-356. 
Easton, Pa. 1906. 

2 Warington, R., and Peake, W. A. On the Determina- 
tion of Carbon in Soils. Jour. Chem. Soc. (London) Trans., 
Vol. 37, pp. 617-62.5. 1880. 

' Briggs, L. J., and others. The Centrifugal Method of 
Mechanical Soil Analysis. U. S. D. A., Bur. Soils, Bui. 24, 
pp. 33-38. 1904. Also, Cameron, F. K., and Breazeale, J. F. 
The Organic Matter in Soils and Subsoils. Jour. Amer. 
Chem. Soc, Vol. 26, pp. 29-45. 1904. 



144 SOILS: PROPERTIES AND MANAGEMENT 

due to the resistance to oxidation ^ by the carbonized 
matter, already discussed. This material, while it suc- 
cumbs to ignition, resists the action of the sulfuric and 
chromic acids to a very large degree. 

97. The estimation of soil humus. — The common 
method of humus estinuition is that proposed by Grand- 
eau.^ The sample of soil is first washed with acid in order 
to remove all bases. It is next treated with ammonia, 
which will then dissolve out the humous materials. By 
catching this percolate, evaporating it to dryness, and 
weighing it, the percentage of humus may be calculated. 
The dark humous extract obtained with the ammonia 
is called the Matiere Noire. 

This method has undergone several modifications,^ of 
which that of Ililgard "* and that of Houston and McBride ^ 
seem the most promising. The method of the latter 
chemists has been adopted by the Association of Official 
Agricultural Chemists and is considered as the official 
method. In the procedure an attempt is made to keep 
the concentration of the ammonia in contact with the 
soil constant during the extraction. Consequently the 
sample, after treatment with the acid, is washed into a 

1 Schreiner, O., and Brown, B. E. Occurrence and Nature 
of Carbonized Material in Soils. U. S. D. A., Bur. Soils, 
Bui. 90, pp. 19-21. 1912. 

- Grandeau, L. Traiti d'Analyse de Matieres agricoles. I, 
p. 151. 1897. 

' A comparison of the various methods is found as follows : 
Alway, F. J., and others. The Determination of Humus. 
Nebr. Agr. Exp. Sta., Bui. 115. June, 1910. 

^ Hilgard, E. W. Humus Determination in Soils. U. S. 
D. A., Div. Chem., Bui. 38 (edited by H. W. Wiley), p. 80. 
1893. 

^ Wiley, H. W. Official and Provisional Methods of Analy- 
sis. U. S. D. A., Bur. Chem., Bui. 107, p. 19. 1908. 



THE ORGANIC MATTER OF THE SOIL 145 

500 cubic centimeter flask, which is filled to the mark 
with 4 per cent ammonia. Digestion is allowed to pro- 
ceed for twenty-four hours, with frequent shakings, and 
and an aliquot portion of the supernatent liquid is taken 
for analysis. This method with its modifications is 
practically the only one that we have for the estimation 
of soil humus. It is based on the fact that when a 
soil is lacking in active basic material, the humous 
matter may be extracted with ammonia. A modification 
of this method may be used as a test for soil acidity, 
as any soil of humid regions allowing the extraction of 
humus by ammonia alone must lack basic materials. 

The composition of the ash constituents of the matiere 
noire is given by Snyder ^ as follows, the data being the 
average of eight analyses : — 

The Ash from the Humus of Minnesota Prairie Soils 

Percentage 

Insoluble 61.97 

FeaOs 3.12 

AI2O3 3.48 

K2O 7.50 

NaaO 8.13 

CaO 09 

MgO 36 

P2O5 12.37 

SO3 98 

CO2 1.64 

The relatively high percentage of phosphoric acid is 
immediately noticeable in this analysis. This indicates 

' Snyder, Harry. Soils. Minnesota Agr. Exp. Sta., Bui. 41, 
p. 30. 1895. 

L 



146 SOILS: PROPERTIES AND MANAGEMENT 

that no mean portion of the soil phosphates is held in 
organic combination. The promotion of favorable hu- 
mous decay must thus liberate a considerable amount of 
phosphorus for plant utilization. 

98. Organic content of representative soils. — The 
organic content of soils varies widely accortling to climatic 
conditions. The following average data show the limits 
of variation as well as the comparative content of the 
important soil sections of the United States : — 

Organic Content of United States Soils 





Sandy Soils 


Clay Loams and Loams 




Soil 


Subsoil 


Soil 


Subsoil 


North Central States . 


1.84 


.76 


3.06 


1.07 


Northeastern States 


1.66 


.60 


3.73 


1.35 


South Central States 


1.16 


.55 


1.80 


.65 


Southeastern States 


.93 


.41 


1.53 


.73 


Semiarid States . . . 


.99 


.62 


2.64 


1.11 


Arid States .... 


.89 


.64 


1.05 


.62 



It is at once apparent that the subsoil contains con- 
siderably less organic matter than do the surface layers. 
Also, the areas of the United States that have been 
glaciated are noticeably richer in organic material than 
the residual, coastal plain, and arid regions. This is 
largely a climatic and geochemical relationship. Some 
soils, particularly alluvial soils, very often run higher 
than the average data given above. An organic content 
of 5 or 6 per cent is not an uncommon figure with such 
materials. jNIuck and peat soils are of course not to be 
classified with the above, as their organic content may 



THE ORGANIC MATTER OF THE SOIL 



147 



range from 35 to 85 per cent, according to the admixture 
of mineral matter from extraneous sources. 

99. The humus content of soils. — The humus content 
of soils is of course lower than the organic matter therein 
contained. It likewise varies according to climate and 
region, not only in amount, but also in composition. The 
following data, compiled from Hilgard,^ illustrate this 
point : — 

The Humus of Arid and Humid Soils 



41 Arid uplands soils 
15 Subirrigated arid soils 
24 Humid soils 



Humus in 
Soil 

(Percentage) 



.91 
1.06 
4.58 



Nitrogen in 
Humus 

(Percentage) 



15.23 

8.38 
4.23 



Nitrogen in 
Soil 

(Percentage) 



.135 
.099 
.166 



It is evident that humid soils not only contain the 
greatest amounts of organic matter, but also excel in 
humus. The humus of the arid regions, however, is 
richer in nitrogen, due to the peculiar decomposition going 
on. As a consequence the nitrogen in the soil of humid 
regions is not greatly in excess of that in the soils of drier 
climates. 

The percentage of humus not only decreases as the 
lower depths of soil are examined, but also changes in 
composition, becoming poorer in nitrogen the deeper 
the soil is penetrated. The following data on a Russian 
river soil, quoted by Hilgard,^ may be cited as an in- 
stance : — 



1 Hilgard, E. W. Soils, pp. 136-137. 

2 Ibid., p. 139. 



New York. 1911. 



148 SOILS: PROPERTIES AND MANAGEMENT 



The Humus of a Russian Alluvial Soil 





Percentage of 

HUMDS 


Percentage of 


Percentage op 


Depth in Feet 


Nitrogen in 
Humus 


Humous Nitrogen 
IN Soil 


1 


1.21 


5.30 


.064 


2 


1.16 


4.32 


.054 


3 


1.14 


3.87 


.044 


4 


1.17 


3.76 


.044 


5 


.74 


2.16 


.016 


6 


.60 


2.66 


.016 


7 


.47 


2.54 


.012 


8 


.78 


1.54 


.012 


9 


.54 


2.24 


.012 


10 


.52 


1.15 


.006 


11 


.53 


1.51 


.008 


12 


.44 


1.81 


.008 



Other depth relationships, especially regarding the 
proportions of carbon, humus, and nitrogen, are brought 
out in the following data, obtained by Alway and Yail ^ 
in the study of Nebraska Soils : — 

Composition of a Nance County, Nebraska, Soil near 

Genoa 



Depth 


Percent- 
age OP 
Nitrooen 


Percent- 
age OP 
Carbon 


Percent- 
age OP 
Humus 


Percent- 
age OP 
Ash in 
Humus 


Ratio of 


IN Feet 


C 

N 


H 

N 


C 
H 


1 
1 
3 
4 
5 
6 


.255 
.102 
.056 
.042 
.034 
.027 


2.61 
.85 
.31 
.24 
.17 
.14 


2.47 
1.00 
.40 
.30 
.19 
.16 


1.61 
.90 
.52 
.64 
.33 
.36 


10.2 
8.3 
5.5 
5.7 
5.0 
5.2 


9.7 

9.8 
7.1 
7.1 
5.6 
5.9 


1.0 
.9 

.8 
.8 
.9 
.9 



1 Alway, F. J., and Vail, C. E. The Relative Amounts 
of Nitrogen, Carbon, and Humus in Some Nebraska Soils. 
Nebraska Agr. Exp. Sta., 25th Ann. Rept., p. 155. 1912. 



THE ORGANIC MATTER OF THE SOIL 



149 



100. Influence of the original material on the resultant 
humus. — It is evident that the source from which any 
humus material is derived will exert a profound influence 
on its composition, especially its nitrogen content. 
Snyder ^ has investigated this by mixing certain materials 
with a soil poor in humus and allowing the process of 
decay to proceed for a year under favorable conditions. 
At the end of the period the humus was extracted by the 
Grandeau method. The results are given below : — 

The Composition of Humus produced from Various Or- 
ganic Materials 



Sugar . . 
Sawdust 
Oats straw 
Wheat flour 
Cow manure 
Green clover 
Meat scrap 



57.84 
49.28 
.54.30 
51.02 
41.93 
54.22 
48.77 



3.04 
3.33 

2.48 
3.82 
6.26 
3.40 
4.30 



39.04 
47.07 
40.72 
40.14 
45.63 
34.14 
35.97 



.08 
.32 
2.50 
5.02 
6.16 
8.24 
10.96 



Although the humiiication may not have reached 
completion in this case, the great variation in nitrogen 
is striking. Existing, as it prol)ably does, mostly as 
acid amides and monamino acids, it will change readily 
to ammonia and exert a marked effect on plant growth. 
Possibly the variation of the nitrogen in soil humus is 
the most potent factor in the nutritive functionings of 
this material. The variability of the carbon, hydrogen, 
and ox;)'^gen of the soil humus is not such an important 
factor, as these elements can easily be supplied to the 



' Snyder, Harry. Production of Humus from Manures. 
Minnesota Agr. Exp. Sta., Bui. 53, p. 25. 1897. 



150 SOTLS: PROPERTIES AND MANAGEMENT 

soil by the plowiiig-uiider of green materials or of barn- 
yard manures. In general, the percentage content of 
inorganic matter increases as the organic matter decays. 

101. Effects of organic matter on soil. — The effects 
of the organic matter on soil and plant conditions are as 
numerous as they are complex. Some of the influences 
are direct, others are indirect. As the specific gravity of 
organic matter is low, the first effect of its addition would 
be to lower the absolute and the apparent specific gravity 
of the soil. As the water capacity of humus is very high, 
a soil rich in organic constituents usually possesses a 
high water-holding power. This makes possible greater 
volume changes both on drying and in the presence of 
excessive moisture. The granulating effects of wetting 
and drying and freezing and thawing are therefore ac- 
celerated. The organic matter tends also to spread 
the individual particles of soil farther apart, especially 
in a clay. Its loosening effects are immediately ap- 
parent in such soil. On the other hand, because organic 
matter has a higher cohesive and adhesive power than 
sand, it performs the function of a binding material 
with the latter soil, a condition much to be desired in a 
material possessing such textural characteristics. 

The better tilth induced by the presence of organic 
matter in any soil tends to facilitate ease in drainage 
and to encourage good aeration. These two conditions 
are of course necessary for the promotion of soil sanita- 
tion. Root extension and bacterial activity are thus 
increased. It is of especial importance that the splitthig- 
up of the organic matter shall take place in the presence 
of plenty of oxygen, in order that toxic compounds may 
not be generated and that a humus highly favorable to 
plant growth shall be produced. The increased water 



THE ORGANIC MATTER OF THE SOIL 151 

capacity of the soil resulting from the presence of organic 
materials is of some importance in drought resistance, 
while the black color imparted by the humus tends to 
raise the absorptive power of the soil for heat. 

The soil organic matter, however, functions in other 
ways than those strictlj' physical. The hmnus or its 
degradation products may serve as plant-food. Bacteria 
and other soil organisms are also furnished a source 
of energy thereby, and the production of carbon dioxide 
is much increased. This carbon dioxide, as well as the 
organic acids generated, tends to raise the capacity of 
the soil water as a solvent agent, and thus the amount of 
mineral plant food available to the crop is greatly in- 
creased. The general effect of organic matter, then, is 
to better the soil as a foothold for plants, and to increase 
either directly or indirectly the available food supply for 
the crop. 

102. Maintenance of soil organic matter. — The main- 
tenance of a proper supply of organic matter in a soil is 
a question of great practical importance, as productivity 
is governed very largely by the humus content of the soil. 
This maintenance of the soil humus depends on two 
factors — the source of supply and methods of addition, 
and the promotion of proper soil conditions in order that 
the organic matter may perform its legitimate functions. 

The organic matter of the soil may be increased in a 
natural way by the plowing-under of green crops. This 
is called green-manuring and is a very satisfactory prac- 
tice. Such crops as rye, buckwheat, clover, peas, beans, 
and vetch lend themselves to this method of soil im- 
provement. Not only do these crops increase the actual 
carbohydrate content of a soil, but in the case of legumes 
the nitrogen also is increased in amount, due to the 



152 SOILS: PROPERTIES AND MANAGEMENT 

symbiotic action of the nodule bacteria. Green-manure 
crops may also protect the soil from loss of plant-foorl by 
leaching. The addition of barnyard manure is a common 
method of raising the organic content from external 
sources, and on decaying this manure performs the same 
function as natural soil humus. Muck, peat, straw, or 
leaves may be used in a similar manner. 

Improper soil conditions not only prevent the proper 
decay of organic matter, l)ut also tend to encourage the 
production of products inimical to plant growth. There- 
fore, in order that organic materials added to any soil 
may produce the proper humous constituents and per- 
form their normal functions, soil conditions in general 
must be of the best. Tile drainage should be installed, 
if necessary, in order to promote aeration and granulation. 
Lime should be added if basic materials are lacking, for 
it promotes bacterial activity as well as plant growth. 
The addition of fertilizers will often be a benefit, as will 
also the establishment of a suitable rotation. The rota- 
tion of crops not only prevents the accumulation of 
toxic materials, but also, by increasing crop growth, 
makes possible a larger addition of organic matter by 
green-manuring. 

Good soil management seeks to adjust the addition 
of organic matter, the soil conditions, and the losses 
through cropping and leaching, in such a way that paying 
crops may be harvested without impairing the humus 
supply of the soil. Any system of agriculture that tends 
to permanently lower the organic matter of the soil is 
impractical, and improvitlent, as well as unscientific. 



CHAPTER IX 
THE COLLOIDAL MATTER OF SOILS ^ 

It has already been noted, in the discussion of the clay 
separate of any soil, that in the presence of water 
certain of the very finest particles, even though apparently 
dissolved, assume particular and important properties, 
such as high adsorption, nondiflFusion through mem- 
branes, and the Brownian movement. Such material 
has been designated as colloidal in nature. It must 
be understood from the beginning, however, that 

1 Some of the following general references may prove of in- 
terest : — 

Freundlich, H. Kapillarchemie. Leipzig, 1909. 

Zsigmondy, R. Kolloidchemie. Leipzig, 1912. 

Bancroft, W. D. The Theory of Colloid Chemistry. 
Jour. Phys. Chem., Vol. 18, No. 7, pp. 549-558. 1914. 

Niklas, H. Die Kolloidchemie und ihre Bedeutung fiir 
Bodenkunde, Geologie, und Mineralogie. Internat. Mitt. 
fiir Bodenkunde, Band II, Heft 5, Seite 383-403. 1913. 

Ramann, E. Kolloidstudien bei Bodenkundlichen Arbei- 
ten. Kolloidchemische Beihefte, Band II, Heft 8/9, Seite 285- 
303. 1911. 

Konig, J., Hasenbaumer, J., und Hassler, C. Bestimmung 
der KoUoide im Ackerboden. Landw. Ver. Stat., Band 76, 
Heft 5/6, Seite 377-441. 1912. 

Noyes, A. A. The Preparation and Properties of Colloidal 
Mixtures. Jour. Araer. Chem. Soc, Vol. 27, pp. 85-104. 1905. 

Thaer, W. Der Einfluss von Kalk und Humus auf die 
Meehanische und Physikalische Beschaffenheit von Ton-, 
Lehm-, und Sandboden. Jour. f. Landw., Band 59, Heft 1. 
Seite 9-57. 1911. Also, Kolloidchemische Studien. Jour, 
f. Landw., Band 60, Heft 1, Seite 1-18. 1912. 

1.53 



154 SOILS: PROPERTIES AND MANAGEMENT 

colloidal material floes not differ from crystalloidal 
in chemical composition, but the distinction is merely 
one of size of particles. For example, if large particles 
are suspended in water, they will immediately sink, 
since their weight is so much greater than the sur- 
face that is exposed for l)uoyance. When these particles 
are decreased in size, their weight decreases much faster 
than the surface exposed. It is therefore e\'ident that 
a point will at last be reached at which the particles, 
because of their minute size, will form a homogeneous 
solution. The upper limit of the colloidal state has then 
been entered. 

103. The colloidal state. — The colloidal state in which 
these particles are now found is a peculiar one, and ex- 
hibits much diversity, not only in properties, but also 
in the size of particle in which the material exists. The 
upi)er limit of the clay grouj) as designated by the classi- 
fication of the United States Bureau of Soils is .005 milli- 
meter, while the upper limit of the particle existing in a 
colloidal state is estimated to be below .005 of a micron, 
or .000005 millimeter. Indeed, so small are the colloidal 
particles that they become molecular complexes, that is, 
a few molecules may go to make up a particle. 
The various" colloids, or the same colloid under different 
conditions, may exhibit greatly differing sizes of particles. 
Some colloidal particles are xcty large, approaching the 
upper limit already set for material in such a state. Other 
particles are finer. It is evident that a gradation must 
exist until a particle is reached which consists of oidy one 
molecule. The solution then ceases to be a molecular 
complex and becomes a true solution. The colloidal 
state thus grades into the true solution, just as an 
ordinary suspension grades into a true, or colloidal, 



THE COLLOIDAL MATTER OF SOILS 155 

suspension. While this method of comparison fails to 
recognize the various phases that colloidal materials 
may exhibit and is therefore faulty in this regard, it 
does lay emphasis on the differences as to size of par- 
ticle that exist between colloidal bodies and materials 
as they are ordinarily recognized. This relationship 
is shown by the following diagram : — 

ORDINARY SUSPENSION | COLLOIDAL STATE | TRUE SOLUTION 

MOLECULAR COMPLEX 

Fig. 22. — Diagram showing the relationship of the colloidal state 
(molecular complex) to ordinary suspensions and true solutions. 

Since colloidal particles vary in size from .005 of a 
micron to a molecule, the range must be very great. 
Just how great cannot be very accurately stated. It 
is interesting to note, however, that this range is much 
greater in proportion than is exhibited between the fine 
gravel and the ordinary clay particles found in soil. With 
this possible difference, it is no great wonder that the 
various colloids exliibit with different intensities the 
characteristics so peculiar to them and of such great im- 
portance in everyday life. The particles in the upper 
range of the colloidal field can be seen with the ordinary 
microscope. As such particles become smaller they cease 
to be visible under the ordinary microscope and can be 
detected only by the ultramicroscope. It is probably 
true that by far the greater proportion of the particles 
of material in a colloidal state cannot be detected by 
microscopic means. This gradation of colloidal materials 
and the extreme fineness of the particles is well illus- 
trated by the following diagram (Fig. 23), although it 
fails to convey any idea regarding the various phases 
that colloids may occupy. 



156 SOILS: PROPERTIES AND MANAGEMENT 




Fig. 23. — Diagram .'showing the pussiljle ruiigu in the size of colloidal 

particles. 

104. The properties of colloids. — Tn general there are 
certain properties wliich materials in a colloidal state 
exhibit and by which they are distinguished from true 
solutions. In the first place, since they are not in 
true solution they exert little effect on the freezing 
point, on vapor tension, and on vapor pressure. Some 
colloids have absolutely no effect on these conditions, 
while others, as they allow a certain small amount 
of true solution to take place, do possess such 



THE COLLOIDAL MATTER OF SOILS 157 

Influences to a slight degree. Secondly, colloids do not 
pass readily through semipermeable membranes, as 
parchment paper, while crystalloids do. This serves as 
a very easy way of separating colloidal and crystalloidal 
material. As a matter of fact, the membrane is itself a 
colloid. Thirdly, heat and the addition of electrolytes 
will serve to coagulate or precipitate certain colloids, a 
property which again serves to distinguish them sharply 
from a true solution. P'ourthly, colloidal material has great 
adsorptive power, not only for water, but also for materials 
in solution, a quality of extreme importance in soil studies. 
It has been shown that a colloid is a material in a 
certain state of division, in which it exhibits properties 
not possessed by an ordinary suspension or by a true 
solution. It is therefore proper to speak of matter so di- 
vided as being in the colloidal state, or colloidal condition. 
It is not to be inferred, because the colloidal phase is 
contrasted with the crystalloidal, that colloids are amor- 
phous. They may or may not be in such a condition. 
Moreover, the same material may exist without chemical 
change either in the colloidal or non-colloidal state. For 
example, silicic acid, ferric hydrate, geld, carbon black, 
and other materials, may or may not be colloidal, ac- 
cording to circumstances. The fineness of division is 
the explanation of colloidal properties. In order to 
place such a discussion on a more understandable basis, 
a few illustrations of the colloidal state will not be amiss. 
The following materials, which may exist as colloids, may 
be for convenience grouped under two general heads, 
organic and inorganic : — 

Organic: Gelatin, agar, caramel, albumin, starch, jelly, 
. humus, carbon black, tannic acid, etc. 



158 SOILS: PROPERTIES AND MANAGEMENT 

Inorganic: Gold, silver, iron, ferric hydrate, arsenious 
oxide, zinc oxide, silver iodide, Prussian 
blue, etc. 

105. Colloidal phases. — In jjeneral, two conditions 
are necessary for the colloidal state — a dispersive medium, 
and a material that will disperse, the latter being usually 
desio;nated as the disperse phase. Three materials may 
function as a dispersive medium — a liquid, a solid, or a 
gas. In the same way, with each dispersive medium there 
may be three disperse phases — a liquid, a solid, or a gas. 
This gives nine general phases to be considered in colloidal 
chemistry. From the soil standpoint, the liquid-solid 
and the liquid-liquid phases are by far the most important 
and will be the only ones to receive detailed attention 
here. In the liquid-solid phase, as with colloidal gold 
or ferric hydrate, the particles are suspended in water 
as the dispersive medium. In the case of gelatin, another 
liquid-solid example, the jelly surrounds the dispersive 
medium, or liquid. An emulsion may exhibit the liquid- 
liquid phase, and possibl}' exists in soils rich in humus. 

In these colloidal phases under discussion and of such 
particular interest in soil study, two general classes of 
materials are found, which seem to differ radically from 
each other and yet are likely to lead to considerable con- 
fusion unless special ])ains are taken to distinguish between 
them. As types, gelatin and a colloidal suspension of 
ferric hydrate may be cited. The gelatin is considerably 
more viscous than water, while the ferric hydrate does 
not differ from water in this respect. The former gelatin- 
izes on cooling or on loss of moisture, but will become 
dispersed again on the addition or ])resence of water. In 
other words, it will pass again and again, back and forth, 



THE COLLOIDAL MATTER OF SOILS 159 

from a sol to a gel. It is what might be called a reversible 
colloid. Moreover, it is not coagulated by ordinary addi- 
tions of salt or by heating. The ferric hydrate colloid, 
on the other hand, when precipitated or agglutinated by 
any means may not easily be brought back again to the 
sol state. It is a so-called irreversible colloid. Moreover, 
it is thrown down by the addition of electrolytes. There 
exist, then, the viscous, gelatinizing, reversible colloids, and 
the non-viscous, non-gelatinizing, easily coagulable, and 
non-reversible colloids, besides all gradations and variations 
between the two. In the ordinary clay soil, both types 
of these materials probably exist and play important parts 
in the physical and chemical characteristics exhibited. 

106. Flocculation. — While the gelatinous colloids of 
the soil, such as some of the humic materials, are not 
agglutinated by the addition of electrolytes, most of the 
colloids of a nature similar to colloidal silicic acid and 
ferric hydrate are thrown down by this treatment. This 
phenomenon is often spoken of as flocculation. A very 
good example is afforded by treating a clay suspension 
with a little caustic lime. The tiny particles almost 
immediately coalesce into floccules, and, because of their 
combined weight, sink to the bottom of the con- 
taining vessel, leaving the supernatant liquid clear. 
The same action will take place in the soil itself, but of 
course with less rapidity and under conditions less notice- 
able to the eye. The colloids thus thrown down, being 
largely irreversible, cannot again assume their former 
attributes and thus lose their distinguishing character- 
istics. In general, acids bring about flocculation while 
alkalies do not, calcium oxide and calcium hydrate being 
the best-known exceptions to the latter. Ammonia is 
an intense deflocculator. 



160 SOILS: PROPERTIES AND MANAGEMENT 

Just how this ])hen()nienon of floccuhition or ag<i:hitina- 
tion may be accounted for theoretically it is rather difficult 
to state. The general theory is one of electrification. It 
is found that certain colloids, when subjected to the 
proper electric current, will migrate to either the positive 
(anode) or the negative (cathode) pole. These particles 
evidently carry a charge of electricity. Ferric hydrate, 
aluminium hydrate, and basic dyes, for example, move 
toward the cathode and carry a positive charge; while 
arsenious sulfide, silicic acid, gold, silver, and acid dyes 
move toward the anode and are negative. It is assumed 
that as long as the colloidal particles remain charged 
they repel each other and the colloidal state persists. 
When an electrolyte is added the ionization is supposed 
to cause a discharge of the repellent electricity carried 
by the colloidal particles, and flocculation or agglutina- 
tion immediately takes place. 

Certain colloids may flocculate certain others, as the 
gelatinization of silicic acid by ferric hydrate. At times 
one colloid may protect another, probably by surrounding 
it with a protective film. Such a case may be shown by 
adding gelatin to a clay suspension. When a colloid such 
as ferric hydrate is flocculated, it loses to a certain extent 
its peculiar properties, and assumes the characteristics of 
ordinary materials. It is evident, therefore, that if the 
properties exliibited by colloidal materials become either 
directly or indirectly detrimental to ])lants, their floccula- 
tion would be beneficial. In field practice this is usually 
accomplished by the addition of lime. The colloidal 
material existing in a normal soil and possessing a gelat- 
inous nature, similar in general to gelatin, is probably 
not all flocculated by the addition of ordinary amounts 
of electrolytes. This material may be influenced by 



THE COLLOIDAL MATTER OF SOILS 161 

drying, whereby it slowly gives off water, becomes more 
and more viscous, and at last may lose its gel qualities 
and become hard and irreversible. It is evident, there- 
fore, that wetting and drying, frost, and the like, become 
factors in dealing with this form of colloidal matter. 

107. Common soil colloids and their generation.^ — 
The common soil colloids may, for convenience, be dis- 
cussed under two heads, organic and inorganic. Of the 
former, the so-called humic acid stands as the example ; 
of the latter, silicic acid, ferric hydrate, and amorphous 
zeolitic silicates are the commonest. 

Organic colloids. — The humic colloids in a normal 
fertile soil probably make up the bulk of the colloidal 
matter. Such material is very heterogeneous, very 
complex, and constantly changing. As yet very little 
study of the organic soil colloids has been made because 
of the difficulties presented by the problem. Humic 
colloids may be viscous or non-viscous, as the case may 
be, and may or may not be thrown down by lime. The 
adsorptive power of these colloids for water, gases, and 
such materials as calcium, magnesium, and potash, is 



^ Van Bemmelen, J. M. Die Absorption. Seite 114-115. 
Dresden, 1910. Also, Die Absorptionsverbindungen und das 
Absorptionsvermogen der Aekererde. Landw. Ver. Stat., 
Band 35, Seite 69-136. 1888. 

Way, J. T. On Deposits of Solnble or Gelatinous Silica 
in the Lower Beds of the Chalk Formation. .Jour. Chem. Soc, 
Vol. 6, pp. 102-106. 18.54. 

Warington, R. On the Part Taken by O.xide of Iron and 
Alumina in the Adsorptive Action of Soils. Jour. Chem. Soc, 
2d ser., Vol. 6, pp. 1-19. 1868. 

Cushman, A. S. The Colloid Theory of Plasticity. Trans. 
Amer. Cer. Soc, Vol. 6, pp. 6-5-78. 1904. 

Ashley, H. E. The Colloid Matter of Clay and its Meas- 
urements. U. S. Geol. Sur., Bui. 388. 1909. 



162 SOILS: PROPERTIES AND MANAGEMENT 

very highly developed — more so, probably, than that 
of the inorganic colloids. These organic colloids are 
formed during the tearing-down and splitting-off processes 
of bacterial activity. Some of the hiimic materials are 
thrown off in a sufficiently fine state of division to assume 
the condition that has been designated as colloidal. Of 
course the chemical forces of weathering are also operative 
in this process of organic colloidal production. 

Mineral colloids. — The inorganic soil colloids, especially 
ferric oxide and silicic acid, are less complex than the 
organic and have been more thoroughly studied. Such 
colloids are generated during the operation of the ordinary 
forces of weathering, especially the chemical phase. For 
example, when a felds])ar undergoes decomposition, the 
following reaction may be used to illustrate the possible 
change that takes place : — 

2 KAlSigOs + 2 HiiO + CO2 = H4Al2Si209 + 4 Si02 + 

K2CO3 

Kaolin practically always has its origin in this way, 
together with an alkali carbonate and silica. The process 
is essentially one of hydration and carbonation ; the CO2 
by reacting with the alkali permits the process to go on. 
The silica may go in three directions, according to con- 
ditions — to free quartz, to hydrated silicates, and to 
colloidal silica. Similar reactions may be written for 
iron and aluminium, but they can only show, as does 
the above, the general trend of the change. In general it 
can be concluded that most inorganic colloids arise from 
ordinary chemical weathering, together with secondary 
minerals of various kinds. Such colloids must be very 
dilute and are difficult to study because of their reaction 
among themselves. 



THE COLLOIDAL MATTER OF SOILS 163 

108. Preparation of colloids. — There are a number of 
methods that may be used in the preparation of artificial 
colloidal solutions, but the description of only one will 
suffice in the present discussion. This is the use of a 
semipermeable membrane. It has already been men- 
tioned that crystalloids pass with ease through a membrane 
such as parchment paper, while colloids do not. It is 
reasonable to expect, then, that these materials may be 
thus separated by proper adjustments. As a matter of 
fact, such a procedure is employed in many cases. The 
operation is called dialysis, and the membrane, itself a 
colloid, is designated as the dialyzing membrane. 

For example, if a solution of ferric chloride to which 
some ammonium carbonate has been added is placed in a 
dialyzer with pure water on the outside, the hydrochloric 
acid and other impurities gradually pass through the 
membrane and a more or less pure colloidal solution of 
ferric hydrate is left behind. The objection to this 
method lies in its extreme slowness. Nevertheless, since 
the cells of plants present a semipermeable membrane, 
this method of preparation serves to exj^lain many actions 
that go on between soil and plant during the processes 
of nutrition. In the soil the formation of colloidal ma- 
terial is entirely a natural exertion of chemical and bio- 
logical forces under such conditions that the particles 
split off are in that state of division which has been desig- 
nated as colloidal. 

It may be inferred that the quantity of colloidal matter 
in an average soil is large, but as a matter of fact this is 
not the case. The proportion of the soil in a colloidal 
state at any one time is very small. It must be remem- 
bered, however, that material is continually being thrown 
out of the colloidal condition and at the same time more 



164 SOILS: PROPERTIES AND MANAGEMENT • 

is generated ; thus the effects may be marked, although 
the amount ])resent at any one time is extremely minute. 

109. Colloids and soil properties. — As may naturally 
be inferred, the influence of the colloidal matter on^ soil 
conditions, especially as related to plants, are extremely 
important. This influence is exerted in two ways. First, 
on cohesion and plasticity ; and, secondly, on the adsorp- 
tive power of the soil. Both these qualities must be con- 
sidered, not only in the physical, but also in the chemical 
and the biological, study of the Voil as a medium for crop 
production. 

In general it is found that, other conditions being equal, 
an increase of colloidal matter increases plasticity ; in 
other words, the ease with which a soil may be worked 
into a puddled condition becomes greater. This is a rather 
undesirable quality when too pronounced, and in clays 
in which it is most likely to be developed some means 
of decreasing the colloidal influence is advisable. This 
great plasticity is developed because the colloids, espe- 
cially those of a gelatinous or viscous nature, facilitate 
the ease with which the particles may move over one an- 
other and yet cohere sufficiently to prevent disruption 
of the mass. In general, also, the greater the plasticity 
of a soil, the greater is the cohesion when dry. In soils, 
then, in which the colloidal material is very high, clodding 
may occur if the soil is tilled too dry because of the great 
tendency of the particles to cohere. This cohesion and 
plasticity, as factors in soil structure, soil granulation, 
and tilth, will be discussed in the succeeding chai)ter. 
It is sufficient at this point only to observe the relation- 
ship of colloidal materials to the development of such 
qualities. 

The second important attribute imparted to soil by 
/ 



THE COLLOIDAL MATTER OF SOILS 165 

colloid development is high adsorptive power. This 
power extends not only to condensation of gases, bnt also 
to water and to materials in solution. The water of 
condensation on dry soil particles when exposed to a 
saturated atmosphere is largely determined by the col- 
loidal content. In other words, the surface exposure of 
colloidal matter is so preponderant in water condensation 
as in a general way to allow the one to be a relative meas- 
ure of the other. Again, colloids exert adsorptive power 
for material existing in the soil water, and to a limited 
extent compete with the plant for food. Until the col- 
loids are satisfied the soil solution may not reach its 
maximum concentration for crop growth. This adsorp- 
tive power is exerted especially on the basic materials, 
such as calcium, and unless the existing colloids are fully 
satisfied the soil tends to become lacking in available 
bases. This condition is generally termed soil acidity. 
It may readily be seen that the concentration of the soil 
solution is governed to a considerable extent by the col- 
loidal content of the soil, and that the adjustments in 
concentration are always toward an equilibrium between 
the two. Colloidal matter does not exert the same adsorp- 
tive power for all materials, but is capable of what might 
be called selective adsorption. For example, if ammonium 
sulfate is added to a soil, the ammonia is strongly taken 
up, which tends to release the sulfate. The continuous 
use of such a fertilizer on a soil poor in lime will ultimately 
result in the presence of free sulfuric acid. This example 
is sufficient to emphasize the relationship of adsorptive 
powers to fertilizer practice. 

110. Factors affecting colloids. — It must not be in- 
ferred from the preceding discussion that the generation 
of colloids is detrimental to soil conditions. In light 



166 SOILS: PROPERTIES AND MANAGEMENT 

soils the presence of such material is extremely necessary, 
as it tends to bind the soil together, facilitates granula- 
tion, and prevents loss of plant food by leaching. It is 
only in heavy soils in which such material is excessive 
that a detrimental condition is likely to exist. This occurs 
because of a high cohesion and plasticity, because of the 
competition for food that is likely to arise with the crop, 
and because of the tendencies toward acidity. Where 
lime is low or lacking, the situation has a tendency to 
become still more aggravated by further colloidal devel- 
opment. 

In general, the practice of underdrainage by allowing 
the wetting and drying of the soil to proceed, is the first 
step not only for the curbing of excessive and improper 
colloitlal influence, but also for the encouragement of 
just the right development thereof. The freezing of 
winter, tillage at proper times, the addition of humus, 
and the application of lime are all practices that aid 
in the control of colloidal conditions. Since this control 
and utilization of colloidal influences is only a phase of 
soil structure as related to tilth- and granulation, a further 
discussion of the subject will be reserved for later consid- 
eration. 

111. Estimation of colloidal content. — The colloids 
in the soil are so complex, so numerous, so variable in 
function, and so susceptible to change, that an exact 
determination of their amount is impossible. The knowl- 
edge of colloidal material in general is so meager that it 
is not surprising that such slight advances have been 
made in fully and clearly determining their character in 
a complicated material, as the soil undoubtedly is. The 
important methods of estimating the colloid content of 
the soil depend for their expression on the intensity of 



THE COLLOIDAL MATTER OF SOILS 167 

certain qualities, supposed to be developed largely by 
colloid content. This indicates that the methods are 
largely comparative, rather than exact or strictly analyti- 
cal in nature. These important methods ^ are three in 
number: Van Bemmelen's, Ashley's, and Mitscherlich's. 

For? Beminelen. — The first investigator to advance 
a method for colloid estimation was Van Bemmelen,^ 
who considered that the amount of silica dissolved from 
a soil by digestion with hydrochloric or sulfuric acids 
was a measure of its colloidal content. It is now known 
that some materials, such as crushed rock, may yield 
as much silica with this treatment as a highly colloidal 
clay. This method is not of great importance at the 
present time, except as to the information that it gives 
regarding the evolution of colloidal soil study. 

Ashley. — A second method, and one of much more 
value, has been evolved by Ashley.^ He found that the 
adsorption of certain dyes by soils afforded a very good 
index to colloidal content. The difficulty in this method, 
however, lies in choosing the most effective dye and regu- 
lating its concentration. Moreover, different colloids 
vary so much in adsorptive capacity for the same dye, 
that only roughly comparative results have thus far been 
possible. 

MitscJierlich. — The third, and as yet the most valu- 

1 A comparison of these methods is found as follows : 
Stremme, H., and Aarnio, B. Die Bestimmung des Gehaltes 
anorganischer Kolloide in Zersetzten Gesteinen und deren 
tonigen Unlagerungsprodukten. Zeitsch. f. Prak. Geol., 
Band 19, Seite 329-349. 1911. 

2 Van Bemmelen, J. M. Die Adsorptionsverbindungen 
und das Absorptionsvermogen der Ackererde. Landw. Ver. 
Stat., Band 35, Seite 69-136. 1888. 

'Ashley, H. E. The Colloid Matter of Clay and Its 
Measurement. U. S. Geol. Sur., Bui. 388. 1909. 



168 SOILS: PROPERTIES AND MANAGEMENT 

able, mode of colloidal estimation is that of Mitscherlich,^ 
in which the adsorptive capacity of the soil is again made 
the comparative index. Water instead of dye is used as 
the adsorbed material. In this method the air-dry soil 
in a thin layer is brought to absolute dryness over phos- 
phorus pentoxide. It is then placed in a desiccator over 
a 10 per cent solution of sulfuric acid and the condensa- 
tion is hastened by a partial vacuum. The sulfuric acid 
is used in order to prevent the deposition of dew on the 
soil. After exposure for about twenty-four hours the 
soils are found to have taken up their maximum moisture 
of condensation, which is called the hygroscopic water. 
The soil is then weighed, and the increase, figured to a 
percentage basis, is taken as a measure of colloidal con- 
tent. The reverse process may also be followed, by 
exposing air dry soil in a saturated atmosphere and 
afterwards drying over phosphorus pentoxide. The 
hygroscopicity of the soil, or its hygroscopic coefficient, 
is thus the basis for colloidal comparison. It is now 
clear why the term colloidal estimation is employed in 
this discussion, rather than colloidal determination. 

An objection to the Mitscherlich method is advanced 
by Ehrenberg and Pick,^ who claim that the drying over 

1 Rodewald, IT., und Mitscherlich, A. E. Die Bestimmung 
der HygroskopizitJit. Landw. Ver. Stat., Band 59, Seite 
433-441. 1903. Also, Mitscherlich, E. A., und Floess, R. 
Ein Beitrage zur Bestimmung der Hygroskopizitat und zur Bewer- 
tung der phvsikolischen Bodenanalyse. Internat. Mitt. f. Boden- 
kunde. Band I, Heft 5, Seite 463-480. 1912. 

2 Ehrenberg, P., und Pick, 11. Beitrage zur phy.sikalischen 
Bodenuntersuchung. Zeit f. Porst- und Jagdwesen, Band 
43, Seite 35-47. 1911. Also, Vageler, P. Die Rodewald- 
Mitscherlichsche Theorie der Hygroskopizitat vom Standpunkte 
der CoUoidchemie und ihr Wert zur Beurteilung der Boden. 
Fiihling's Landw. Zeit., Band 61, Heft 3, Seite 73-83. 1912. 



THE COLLOIDAL MATTER OF SOILS 169 

phosphorus pentoxide will coagulate certain colloids and 
lower their adsorptive power, thus causing the hygro- 
scopic coefficient to become an unreliable comparative 
figure. They suggest first the exposure of the field 
soil over the water and sulfuric acid, and then the ex- 
traction of the hygroscopic water over phosphorus pent- 
oxide. Since this modification is very slow, the original 
Mitscherlich method, in spite of its faults, remains the 
most valuable up to the present time. 



CHAPTER X 
SOIL STRUCTURE 

While texture is the term used in reference to the size 
of the particles in a soil mass, the word structure is em- 
ployed in reference to the arrangement of the grains. 
The structural condition of the soil is very important to 
plant growth, since the circulation of air and water are 
so necessary to normal development. The structural 
condition may be loose or compact, hard or friable, granu- 
lated or non-granulated, as the case may be. Of these 
conditions, granulation, especially in heavy soils, is of 
vital importance, since it is really a simimation of all 
favorable structural conditions. By granulation is meant 
the drawing together of the small particles around a 
suitable nucleus, so that a crumb structure is produced. 
The grains thus cease to function singly. The impor- 
tance of such a structural condition on a heavy soil is 
very obvious. The soil becomes loose because of the 
larger units, air moves more freely, and water not only 
drains away readily when in excess, but responds with 
celerity to the capillary pull of the plant. Before the 
promotion of granulation and the factors that function 
therein may be clearly discussed, however, two properties 
of particular importance, especially in soils of fine tex- 
ture, must be considered. These properties are plasticity 
and cohesion. 

112. Plasticity. — Any material which allows a change 
of form without rupture, and which will retain this form 

170 



SOIL STRUCTURE 171 

not only when the pressure is removed, but also when dry, 
is said to be plastic. Putty with a proper admixture of 
oil is a very good example of a plastic body. As is well 
known, the various plastic materials differ in their plastic- 
ity. Not only this, but such substances as clay or some 
other soils vary in plasticity with their moisture content, 
their granulation, and their texture. The great diffi- 
culty in the study of plasticity has been in finding a 
means of estimation allowing an exact numerical expres- 
sion. The amount of hygroscopic water that a soil will 
hold has been used as an expression of plastic qualities, 
as well as shrinkage on drying, the ability to adsorb dyes, 
tensity, and other characteristics. None of these has 
proved satisfactory, since one quality of a clay or other 
soil is used as a measure of another quality. 

Atterberg ^ has suggested that the difference in mois- 
ture content of a clay at the point at which it ceases to 
be plastic, as compared with the moisture content at 
which it becomes viscous, might be used as an expres- 
sion of plasticity. He has called this figure the plasticity 
coefficient. Thus, a soil may cease to be plastic at 20 
per cent of moisture and may flow at 40 per cent. The 
plasticity coefficient would then be 20. While this is one 
of the latest methods, it is open to the objection already 
stated — that one quality of a soil is used as a measure 
of another. Two soils showing the same plasticity coeffi- 
cient by this method may exhibit undoubted differences 
in actual plasticity. Kinnison,^ in testing several methods 
of expression, found Atterberg's no better than others 

1 Atterberg, A. Die Plastizitat der Ton. Internat. 
Mitt. f. Bodenkundo, Band I, Heft 1, Seite 10-43. 1911. 

^ Kinnison, C. S. A Study of the Atterberg Plasticity 
Method. Trans. Amer. Cer. Soc, Vol. IG, pp. 472-484. 1914. 



172 SOILS: PROPERTIES AND MANAGEMENT 

already in use. For all practical purposes in soil dis- 
cussions, general descrijrtiAe terms may be employed. 

113. The cause of plasticity. — Exactly what may be 
the cause of plasticity has long been under discussion. 
The various theories advanced may be grouped under the 
following heads : ^ — 

A. Structure of clay particles 

1. Fineness of grains 

2. Plate structure 

3. Interlocking particles 

4. Sponge structure 

B. Presence of hydrous aluminium silicates 

C. Molecular attraction between particles 

D. Presence of colloidal matter 

Of. these theories accounting for the plasticity of cer- 
tain bodies, that of colloid content seems the most rea- 
sonable.^ The presence of gelatinous colloidal matter, 
with a certain optimmn amount of water, seems to facili- 
tate the ready movement of the particles while at the 
same time exerting sufficient force to prevent the body 
from splitting apart at the time of movement, or when 
the pressure is removed or the material dried. Thus, 
in general, other conditions remaining equal, materials 
become more plastic the greater the content of colloidal 
matter. In general the colloids function as a measure 
of plasticity. The consideration of shrinkage, hygro- 

• Davis, N. B., The Plasticity of Clay. Trans. Amer. 
Cer. Soc, Vol. 16, pp. 65-79. 1914. 

2Cushman, A. S. The Colloid Theory of Plasticity. 
Trans. Amer. Cer. Soc, Vol. 6, pp. 6.5-78. 1904. Also, Ashley, 
H. E. The Colloid Matter of Clay and Its Measurement. 
U. S. Geol. Survey, Bui. 388. 1909. 



SOIL STRUCTURE 173 

scopic water, and dye adsorption as an expression of 
plasticity become logical on this basis. 

114. The importance of plasticity. — Plasticity assumes 
considerable importance in a soil when it becomes highly 
developed, since it promotes ease in puddling. The 
more plastic a soil is, the more likely it is to become pud- 
dled by tillage, especially if it has a high moisture con- 
tent. Thus a clay cannot be plowed wet, since this 
would allow its particles to be worked into that very intri- 
cate condition so detrimental to plant growth. A sand, 
on the contrary, may be stirred even when saturated, 
and still its structural condition will not be impaired 
since its plasticity is low or nihil. A very plastic soil 
is also likely to become exceedingly hard when dry unless 
it is well granulated, which shows the great care demanded 
by soils having high plasticity coefficients. 

The three factors that affect plasticity to the greatest 
extent are texture, granulation, and moisture. In gen- 
eral, the finer the texture of the soil, the higher is the 
maximum plasticity thereof. The more granular a soil, 
the lower is the plasticity or the tendency to puddle 
when plowed. The amount of water is the third vital 
factor. A soil will exhibit its maximum plasticity at a 
definite moisture content. This point will lie somewhere 
between the flowing, or viscous, condition and the point 
at which a soil refuses to mold, or, in other words, to be- 
come crumbly. With a soil such as a clay, in which the 
plasticity is high, plowing should be done when the 
moisture condition is such that there is no likelihood of 
puddling, and yet the soil will turn over with a maximum 
granulating eft'ect. 

115. Cohesion. — Very closely correlated with plas- 
ticity, but not in exact similarity, is cohesion. By the 



174 SOILS: PROPERTIES AND MANAGEMENT 

cohesion of a soil is meant the tendency that its particles 
exhibit in sticking together and in conserving the mass 
intact. In general, the greater the plasticity of a soil, 
the higher is its cohesion, especially when it is dry or 
only slightly moist. For that reason, cohesion might 
be made a rough measure of plasticity. Cohesion of a 
soil occurs under two general conditions, the wet and the 
dry. When a soil is moist its cohesion is developed by the 
moisture films and the colloidal materials that may be 
present. This form of cohesion is often spoken of as 
tenacity. When a soil is dry its cohesion is developed to 
some extent by the interlocking of its grains and the dep- 
osition of cementing salts. The greatest force is devel- 
oped, however, by the drying and shrinking of the 
gelatinous colloidal matter. As a general rule, the greater 
the amount of colloidal material, the more firmly the soil 
is bound together when dry, or, in other words, the greater 
is its cohesion. 

Cohesion is important in tillage operations, in that 
soils having a high coefficient of cohesion tend to become 
cloddy when plowed and may thus be rendered poor in 
physical condition. This may be avoided by timing the 
operation so that the moisture content is somewhere 
above the point at which excessive cohesion is exerted. 
As cohesion is not greatly developed, except in a heavy 
soil, it is only where fine texture is found that such a 
danger exists. As already shown, the danger is a double 
one, for, since high plasticity and high cohesion go to- 
gether, a soil plowed too wet may puddle while one 
plowed too dry may clod. 

116. Methods of determining cohesion. — A number 
of methods have been devised for determining the co- 
hesion of clavs and other soils. One of the earliest was 



SOIL STRUCTURE 175 

Schiibler's/ in which was tested the resistance of rec- 
tangular prisms of dry soils to penetration by a steel 
blade. The apparatus consisted of a beam supported 
on a fulcrum more than one third of the distance 
from the end. A pan for holding the weights added 
for causing the crushing was hung at the end of the 
long arm, while a counterpoise on the short end of the 
beam acted as a balance. The steel knife was placed 
on the long end of the arm near the fulcrum. The dry 
soil prism was placed under the knife and weights were 
added to the pan until crushing occurred. The weight 
necessary was designated as the cohesion coefficient of 
that soil. 

Haberlandt ^ measured cohesion by crushing soil 
cylinders of a definite size. A glass vessel was placed 
on the top of the column and water was added until the 
column gave way. The weight necessary to bring this 
about was designated as the absolute cohesion of the 
sample. Haberlandt also measured cohesion of soil 
cylinders of a definite size b}' determining the resistance 
to breaking under a transverse load, the soil column being 
placed across supports six centimeters apart. On the 
column midway between the ends a scale pan was sup- 
ported, into which weights were put until breaking oc- 
curred. The figure thus obtained was called the relative 
cohesion. 

1 A good description of Sehiibler's apparatus is found on page 
104 of Bodenkundc, by E. A. Mitscherlich, published by Paul 
Parey, Berlin, in 1905. 

^ Haberlandt, H. Ueber die Koharescenz Verhaltnisse 
versehiedcner Bodenarten. Forsch. a. d. Gebiete d. Agri.- 
Physik., Band I, Seite 148-157. 1878. Also, Wissenschaftlich 
praktische Untersuchungen auf dam Gebiete des Pflanzenbaues, 
Band I, Seite 22. 1875. 



176 SOILS: PROPERTIES AND MANAGEMENT 

Puchiier ^ used a penetration apparatus, consisting 
of a vertical shaft held by metal guides and counterpoised 
by a weight hung over a pulley. The shaft was armed 
at the lower end with a cutting blade, while the upper 
end carried a scale pan for holding the necessary weights 
for penetration. The cohesion coefficient was the weight 
necessary to force the blade a certain distance into the 
soil. All important apparatus have been modeled after 
either Puchner's or Schiibler's. That of Atterberg ^ (see 
Fig. 24) follows the former, while that of the Bureau of 
Soils ^ (see Fig. 25) resembles the latter. 




FiQ. 24. — Atterberg's apparatus for determining the cohesion of soil 
prisms. The soil prism is placed between the cutting edge (A") and 
the sharp plunger (P). Weights are added at (IF). (C) is a coun- 
terpoise. 



1 Puclmer, 11. Untersuehungen iiber die Kohareszenz der 
Bodenarten. Forseh. a. d. Gebiete d. Agri.-Physik., Band 12, 
Seite 195-241. 1889. 

^ Atterberg, A. Die Konsistenz und die Bindigkeit der Boden. 
Internat. Mitt. f. Bodenkunde, Band II, Heft 2-3, Seite 149- 
189. 1912. 

' Cameron, F. K., and Gallagher, F. E. Moisture Content 
and Physical Condition of Soils. U. S. D. A., Bureau of Soils, 
Bul. 50. 1908. 



SOIL STRUCTURE 



177 



Recently Puchner ^ has found a machine for measuring 
the crushing strength of dry soil cylinders to be of value 
in determining the absolute, or maximum, cohesion of 
soils. The results, as he has already demonstrated in 
his previous work, are comparable, in relative value at 
least, to those obtained by simpler methods. 

The great difficulty encountered in measuring the 
natural cohesion of a soil, either wet or dry, is not so 




Fig. 25. — The apparatus used by the United States Bureau of Soils 
for determining the penetration of soils. (C) is mechanically packed 
soil ; (A), steel point ; (P), pail for receiving sand from funnel (F). 
(W) is a counterpoise. 

much in the accuracy of the determination as in controlling 
physical conditions. The cohesion of a soil depends 
very much on the handling it has received in the prepara- 
tion, in the amount of water that is added, and in the 
amount and length of time of drying. Natural granu- 
lation cannot be secured. The Bureau of Soils attempted 
to ob\'iate these difficulties by mechanical sifting and 
packing, but the results were abnormal, due to the sift- 
ing process. As a consequence, most cohesion results 

1 Puehner, H. Vergleichende Untersuchungen iiber die 
Kohareszenz verschiedener Bodenarten. Internat. Mitt, fiir 
Bodenkunde, Band III, Heft 2-3, Seite 141-239. 1913. 



178 SOILS: PROPERTIES AND MANAGEMENT 

have been determined either on samples that have been 
worked to a maximum plasticity and then brought to 
the required moisture content, or on uniformly compacted 
samples that have been allowed to take up water by capil- 
larity. In general the curve that would occur with normal 
granulation, while lower, will follow the direction of a 
maximum plasticity curve. 

117. Factors affecting cohesion. — It is obvious, from 
what has already been said regarding the general char- 
acteristics of soils, that texture must play an important 
role in the determination of the cohesion factor. In 
general, the finer the texture, the greater is the cohesion, 
since, whether the soil is wet or dry, the forces that tend 
to hold the particles together are stronger than in a coarser 
soil. The drier the soil, however, the greater is the tex- 
tural influence in this regard, due to the very great in- 
crease in the binding capacity of the colloidal matter 
on drying. In a coarse soil this binding effect is small or 
entirely absent. 

Another factor is the granular condition of the samples. 
In general granulation may be said to be due to an exer- 
tion of cohesion between a limited number of particles, 
resulting in a crumb, or granular, structure. This granu- 
lation, by loosening the soil mass, lowers not only plastic- 
ity but cohesion also. The addition pf organic matter 
to a soil, by hastening and increasing granidation, will 
tend to lower cohesion at every moisture content ranging 
from a dry to a saturated condition. The following 
data, taken from Puchner,^ bring out the points just 
discussed : — 

1 Puehner, H. Untersuchuugen iiber die Kohareszcnz der 
Bodenarten. F'orsch. a. d. Gebiete d. Agri.-Physik., Band 12, 
Seite 195-241. 1889. 



SOIL STRUCTURE 



179 



Effects of Texture, Granulation, Humus, and Moisture 
ON Cohesion op Soils. (Puchner.) 



Clay 

2 clay + 1 quartz 

1 clay + 2 quartz 
Quartz 

2 clay + 1 humus 
1 clay + 2 humus 

Humus 

Pulverized loam . 
Granulated loam 

(granules .5-9 mm. 
diam.) . . . . 



Penetration in Grams at Various 
Moisture Contents 




114 
30 

85 
167 

44 

59 
115 

35 



58 



2,404 
437 

1,887 
2,937 

754 
1,010 
1,414 

272 



85 



9,537 
6,304 
3,803 
4,237 
4,704 
1,704 
1,904 
775 



115 



11,870 
12,370 
10,003 
5,137 
7,204 
4,204 
1,804 
1,408 



492 



15,037 

13,204 

13,703 

8,370 

9,537 

5,070 

870 

8,125 



20,037 

15,704 
6,057 
2,370 

12,037 

1,637 

487 

12,358 



1,342 




9^ /^ o /oo 



Fig. 26. — The effects of texture, humus, and moisture on the cohesion 

of soils. 



180 SOILS: PROPERTIES AND MANAGEMENT 



The relationships aheady spoken of are especially well 
shown by the curves (see Fig. 26), particularly the ellect 
of the moisture content on cohesion. In a heavy soil the 
cohesion increases steadily from a saturated condition until 
dryness is reached, the increase becoming accelerated as 
the percentage of moisture decreases. This is because 



4o 



30 



20 




/o 



A^ 9^ 



Fig. 



27. — The cohesion curves of clay and fine sandy loam at various 
moisture contents. (C), point at which soil changes in color. 



SOIL STRUCTURE 181 

the binding power of the colloidal material is greatly 
augmented by desiccation. In a coarse soil such as 
quartz, in which there is very little colloidal matter, the 
cohesion is developed principally by the water film. As 
this thins, its pulling power increases and the curve 
ascends; but when the soil dries this film disrupts and 
the curve drops again, having no colloidal binding ma- 
terial. The same relationships are shown by curves (see 
Fig. 27) adopted from recent determinations by Atter- 
berg.^ 

118. Moisture limits for successful tillage. — In heavy 
soils, in which the colloidal content is usually high, plas- 
ticity and cohesion also are high. This means that the 
soil when too moist will be puddled by tillage implements, 
especially such as the plow, and when too dry clodding 
will occur because of very high cohesion. A moisture 
limit must therefore exist on a heavy soil, within which 
successful plowing may be done and maximum granu- 
lation results may be secured. That this moisture limit 
is narrow is obvious, since high cohesion and high plas- 
ticity bound it so closely on either hand. Such a rela- 
tionship must be kept in mind not only by the farmer 
but by the technical man as well, since so much depends 
in any work upon good soil tilth. The relationship is 
clearly shown by the following curves (Fig. 28) partially 
adopted from Atterberg.^ The cohesion and plasticity 
curves are seen to cross near the center of the diagram 
and indicate the existence of a zone where neither are 
exceedingly high or low. 

In a clay soil a study of the optimum moisture condi- 

1 Atterberg, A. Die Konsistenz Kurven der Mineralboden. 
Internat. Mitt. f. Bodenkunde, Band IV, Heft 4-5, Seite 418- 
431. 1914. 



182 SOILS: PROPERTIES ANT) MANAGEMENT 



\C0H£5f0n 










PLASTICITY 


X 

\ X 

X 










,^^ 



Fig. 28. — Diagram showing the moisture limits for successful plowing 
in soils of different class, cc and hh' represent the moisture limits 
within which successful plowing may be accomplished on a clay and 
humus clay respectively. 



tions is necessary in order to determine Avhat is just the 
right moisture content for good plowing. That this 
condition . must be carefully gauged and immediate use 
made of the advantages it offers is shown by its narrow 
limit. A few days may suffice for the moisture to drop 
through such a narrow area of fluctuation. A clay soil is 
so difficult to handle at best that no opportunities such as 
are offered by optimum moisture conditions should be lost. 
Moreover, a heavy soil plowed too dry or too wet does not 
regain its normal granular condition for several seasons. 
In a sandy soil no such difficulties are encountered. 



SOIL STRUCTURE 183 

Since the soil has low cohesion, plowing when it is too 
dry will not clod, while, because of low plasticity, little 
puddling will occur if tillage is in progress when the soil 
is wet. Being always rather loose, such a soil is often 
benefited by plowing when it is slightly wet, the parti- 
cles being brought into closer contact and excessive per- 
colation being stopped while at the same time the water 
capacity is raised. 

119. Control of cohesion and plasticity. — It is evi- 
dent not only that cohesion and plasticity control the 
successful tillage of the land, especially where the soil 
texture is fine, but also that these same factors vary with 
the moisture and the granular structure of the soil. It 
has been shown that there is a moisture zone in all soils — 
this being narrower the finer the soil texture — at which 
neither cohesion nor plasticity is excessive. In this zone 
a heavy soil may be successfully plowed, with results 
favorable to the structural condition of the soil. Since 
the processes of granulation have already been shown to 
lower cohesion and plasticity, it is evident that as a crumb 
structure is developed the moisture zone for proper plow- 
ing will be widened, especially in a heavy soil. This is a 
very important point in the handling of clays and clay 
loams, since it not only opens a way for the elimination 
of the dangers of bad structural relationships, but also 
provides for putting the soil in a condition for easier and 
more convenient tillage. In a sandy soil, particularly 
where humus is the granulating agent, a soil with 
more cohesion, more plasticity, and a greater water- 
holding power is developed, all of which tend toward a 
better medium for plant growth. Methods of develop- 
ing this granulation thus become the logical topic for 
further discussion. 



184 SOILS: PROPERTIES AND MANAGEMENT 

120. Soil tilth. — The previous data and discussion 
have clearly shown the very great importance of a crumb 
structure in the working of the soil in the field. Since 
good physical condition will reflect itself on crop yield, 
it is evident that structure must ultimately be considered 
in relation to all plant growth. This relationship is 
usually expressed by the term tilth. While structure 
refers to the arrangement of the particles in general, and 
granulation to a particular aggregate condition, tilth 
goes one step further and includes the plant. Tilth, then, 
refers to the physical condition of the soil as related to 
crop growth. It may be poor, medium, good, or excel- 
lent, according to circumstances. Good tilth may de- 
mand in some soils maximum granulation, in others 
only a medium development. ]\Iaximum tilth always 
implies the presence of water, since the best physical 
relationships cannot be developed without optimum 
moisture conditions. 

From the curves already presented, it is evident that 
an optimum moisture condition exists for the proper 
tillage of a soil, especially one of a heavy character. Also, 
an optimum moisture condition must exist for proper 
tilth, and therefore for proper plant development, since 
adequate tilth is the best physical condition for crop 
growth. Practical experience and theoretical evidence ^ 
have shown that these two optimum conditions are 
identical in nearly all cases, a happy coincidence in the 
practical management of a soil. The optimum moisture 
condition for plant growth, then, is the proper moisture 
condition for effective plowing. The optimum condition 

1 Cameron, F. K., and Gallagher, F. E. Moisture Content 
and Physical Condition of Soils. U. S. D. A., Bur. Soils, Bui. 
50, p. 8. 1908. 



SOIL STRUCTURE 185 

for developing a favorable crumb structure is obviously 
the optimum moisture content for the development of 
the highest tilth. In fact, it can be stated with certainty 
that the optimum moisture condition for plant growth 
is the optimum for all favorable soil activities, whether 
physical, chemical, or biological. Granulation, then, 
becomes the vital factor in placing the soil in a physical 
condition such that the highest tilth, that physical criterion 
which every farmer should strive for, may be developed 
in any soil. Until proper granulation is reached, no soil 
can be expected to yield maximum paying returns. 

121. Granulation. — While it is possible to Hst the 
factors that bring about granulation in a soil, it is diffi- 
cult to state specifically just why this phenomenon takes 
place. It has been suggested that much of the granule 
formation in the soil is due to the contraction of the 
moisture film around the particles when, for any reason, 
the moisture content is reduced (see Fig. 29) . . It is known 




Fig. 29. — A puddled and a well-granulated soil. 

that the soil particles tend to be drawn together by this re- 
duction in the soil moisture, due to the pulling power of the 
thinned film. If to this condition is added a material which 
tends to exert not only a drawing power on loss of mois- 
ture, but also a binding and cementing power when dry, all 



186 SOILS: PROPERTIES AND MANAGEMENT 

the essentials for successful granulation are present. This 
second force is found in the colloidal material present in 
considerable quantities in heavy soils. These are the same 
forces that have already been shown to determine the 
cohesion and plasticity of the soil, except that in granu- 
lating operations they are localized at numberless foci, 
and clodding or puddling is thereby prevented. It is 
evident that if cohesion and jilasticity forces are to func- 
tion for granulation — or, in other words, locally in the 
soil instead of generally and uniformly as when clodding 
or puddling occurs — a certain moisture content must 
be maintained. From what has already been shown, 
it is hardly necessary to restate that this moisture condi- 
tion is near the optimum moisture content for plant 
growth. 

Warington ^ attributes granulation to unequal expan- 
sion and contraction of the soil mass, due to the imbibi- 
tion and loss of water. In a soil subject to such a condi- 
tion, the cohesive forces being localized, the internal 
strains and pressures are unequal and a tendency arises 
for the mass to divide along lines of weakness into groups 
of particles. The binding capacity of colloidal material, 
as well as of salts deposited from the soil solution, tends 
to make such a crumb structure more or less permanent. 
Tillage operations, development of roots, burrowing 
of animals and insects, the presence of humus, and the 
formation of frost crystals, may assist in further develop- 
ing these lines of weakness in the soil mass, on which the 
tension of the moisture films around the soil ])articles is 
brought to bear. The flocculation of soil jjarticles may 
also develop lines of cleavage by their aggregation around 

1 Warington, R. Physical Properties of Soils, pp. 36-41. 
Oxford. 1900. 



SOIL STRUCTURE 187 

certain centers. This movement of the soil particles is 
in every case facilitated by the presence of a moderate 
amount of moisture. 

122. Forces facilitating granulation. — Granulation is 
nothing more or less than a condition brought about by 
the force exerted by a variable water film and the pull- 
ing and binding capacities of colloidal material, operating 
at numberless localized foci. It is evident that any influ- 
ence or change in the soil which will cause a greater locali- 
zation of these operative forces will promote increased 
granulation. The addition of materials from extraneous 
sources is also a practice that may tend to develop lines of 
weakness and thus cause a more intense localization of 
the forces at work. 

The conditions, additions, and practices tending to 
develop or facilitate a granular structure in soils may be 
listed under six heads : (1) wetting and drying of the soil, 
(2) freezing and thawing, (3) addition of organic matter, 
(4) action of plant roots and animals, (5) addition of 
lime, and (6) tillage. 

123. Wetting and drying. — The drying of a soil has 
been shown to result in a drawing together of the particles 
into aggregates. When this process is repeated again 
and again by alternate wetting and drying, the influence 
on granulation becomes marked. 

In drying, the small particles are moved into the spaces 
between the larger ones, thereby reducing the volume 
as is shown by the checks produced. These checks that 
result from shrinkage are due to the unequal contraction. 
There comes a time when the general film around the 
whole mass must rupture, and it breaks along the hues 
of least resistance. If the soil mass is very uniform, there 
will be few breaks and the shrinkage will be mainly around 



188 SOILS: PROPERTIES AND MANAGEMENT 

a relatively few centers. This process produces clods, 
or " overgrown " granules. If there are numerous lines 
of weakness, however, there will he many centers of con- 
traction, and consequently a larger number of small 
clods, or granules, will be fonned. This is the desira})le 
condition and constitutes good tilth — that is, the most 
favorable physical condition for plant growth. 

Just what may be the effects of wetting and drying on 
the colloidal matter of soil is a question. In general, 
desiccation tends to flocculate colloids and in many cases 
their binding power becomes highly developed thereby. 
If such colloids are irreversible, as many in the soil un- 
doubtedly are, this binding becomes more or less per- 
manent, which explains the tendency for a crumb struc- 
ture to persist. Wetting, on the other hand, tends to 
develop colloidal matter which will become binding mate- 
rial on the next drying. The desiccation and throwing 
down of colloids, as well as their generation, thus be- 
comes a very important factor in the wetting and drying 
as related to granulation. 

The following figures ^ rej^resent the relative force 
necessary to penetrate puddled clay dried once, as com- 
pared with the same puddled soil wet and dried twenty 
times. The relative hardness may be taken as a rough 

measure of granulation : — 

Percentage of pene- 
tration 

1. Puddled clay dried once .... 100.0 

2. Puddled clay dried twenty times . 'MA 

3. Puddled clay dried twenty times . 30.6 

4. Puddled clay dried twenty times . 32.0 

• Fippin, E. O. Some Causes of Soil Granulation. Trans. 
Amer. Soc. Agron., Vol. 2, pp. lOG-121. 1910. 



SOIL STRUCTURE 189 

The fact illustrated above has many practical appli- 
cations. It should be observed that the change in struc- 
ture is not associated with continual wetness, nor is it 
identified with a continued dry state. In neither condi- 
tion is any force brought to bear on the particles. The 
force is exerted only during the drying process and the 
wetting process. It is a well-known fact that soils which 
are continually wet are usually in bad physical condition. 
In the drainage of wet land, it is found that the soil is at 
first very refractory ; but when good drainage is estab- 
lished there is a gradual amelioration of the physical 
condition, which is primarily a change in structure. On 
the other hand, in a soil continually in a dry state there 
is no change in granulation. The improvement of soil 
structure, as a result of changes in the moisture content, 
is dependent largely on lines of weakness in the soil mass. 
Some of these are produced in the process of drying, and 
others in the ways already listed. 

124. Freezing and thawing. — As will be seen in 
the consideration of soil moisture, the water is distributed 
in the fine pores of the soil. When it freezes it forms long, 
needle-like crystals. This crystallizing force is very 
great, amounting to about 150 tons when a cubic foot of 
water changes to ice. In freezing, the crystals gradually 
grow first in the larger spaces. During this process there 
is a marked withdrawal of moisture from the smallest 
spaces, so that the ice crystals in the large spaces may be 
built up. The soil mass is separated by the crystals, and 
as the result of even a single hard freeze a wet, puddled soil 
is shattered into pieces. The repetition of this process by 
subsequent freezing and thawing will further break up the 
soil by creating new lines of weakness. The granulating 
power of freezing and thawing is shown in the following 



190 SOILS: PROPERTIES AND MANAGEMENT 

figures,^ expressed as tlie relative force necessary to 
penetrate a puddled clay treated in various ways : — 

Percentage 
penetration 

1. Puddled clay dried once lOO.O 

2. Puddled clay frozen once and dried once . . 30.3 

3. Puddled clay frozen three times and dried once 27.3 

4. Puddled clay frozen five times and dried once . 21.8 

Freezing probably affects the colloidnl material in 
the same general way as does drying. This has been 
indicated by the work of certain investigators,^ in which 
it was foiuid tliat lowering the temperature of a soil below 
freezing lowered the hygroscopic coefficient. 

125. Addition of organic matter. — Soils rich in humus 
or decomposed organic matter are generally in better 
physical condition than soils low in organic content. 
The marked effect of the absence of this material in many 
long-cultivated soils is well known. For example, in 
much of the southern New York hill regions, the soils 
are now recognized to have a very different relation to 
crop growth from what they had for a few years after 
they were cleared. Their color has become lighter, and 
with the decay of the humus a decided physical change 
has taken place in the soil, which is to some extent cor- 
rected by the restoration of the organic content. In 
certain prairie soils the effect of humus depletion on struc- 

1 Fippin, E. O. Some Causes of Soil Granulation. Trans. 
Amer. Soc. Agron., Vol. II, pp. 106-121. 1910. 

- Czormak, W. Ein Bcitrag zur Erkenntiiis der Voriin- 
derungcn der Sog. physikalischen Bodoneigenshafton dureh 
Frost, Ilitze, und die Beigabe einiger Salzo. Landw. Ver. 
Stat., Band 76, Heft 1-2, Seite 73-116. 1912. Also, Ehreaberg, 
P., und Romberg, G. F. von. Zur Frostwirkung auf den Erd- 
boden. Jour. f. Landw., Band 61, Heft 1, Seite 73-86. 1913. 



SOIL STRUCTURE 191 

ture is even more marked. While the actions of humus 
are many, as has already been shown, its rehitionship to 
physical condition is always particularly emphasized. 

Humus contains much colloidal material and in this 
way possesses a certain degree of plasticity. It is, how- 
ever, of a very loose structure and the large spaces con- 
stitute lines of weakness. Another property of humus is 
that it undergoes great change in volume when dried 
out — a property akin to the fineness of the soil, producing 
larger shrinkage cracks. This is noticeable in many 
black clay soils, which check excessively. The great 
capacity of humus for moisture permits a wide range in 
moisture content, which produces corresponding physical 
alteration. This wide swing from one extreme to another 
is a potent factor in granulative influences. The color 
of the humus affects the color of the soil, and thereby 
increases the rate of change from the w^et to the dry state 
by increased evaporation of moisture. The relative 
effects of cnide muck, and the ammonia extract from the 
same muck, on the cohesion of a puddled clay, as indi- 
cated by the force required for a uniform penetration of 
a knife-edge, is showm in the following table ; the samples 
were dried and rewetted twenty times : — 

Puddled Clay plus Muck ^ 

Percentage 
of penetration 

100 

82 

73 

58 

50 



1. Clay 

2. Clay plus 5 per cent of muck 

3. Clay plus 15 per cent of muck 

4. Clay plus 25 per cent of muck 

5. Clay plus 50 per cent of muck 



1 Fippin, E. O. Some Causes of Soil Granulation. Trans. 
Amer. Soc. Agron., Vol. 2, pp. 106-121. 1910. 



192 SOILS: PROPERTIES AND MANAGEMENT 

Puddled Clay plus Muck Extract ' 

Percentage 
of pene- 
tration 

1. Clay 100 

2. Clay plus 1 per cent of extract 85 

3. Clay plus 2 per cent of extract 76 

4. Clay plus 4 per cent of extract 69 

126. Action of plant roots and animals. — The exten- 
sion of plant roots chani;es the soil structure by forcing 
the particles apart at each growing root point, and possibly 
also by some action yet to be explained. Crops differ 
greatly in their effect on soil structure. Grass, millet, 
wheat, and other plants with fine roots are more beneficial 
to tilth than coarse or tap-rooted j)lants such as corn, 
oats, and beets. Grass affects structure also by protecting 
the surface of the ground. It is advisable to establish 
a rotation on clay soil, that plowing may be done at fre- 
quent intervals and that plants with different root devel- 
opments may be given an opportunity to exert their 
influences. The organic matter left in the soil by 
decaying roots is always in very intimate contact 
with the soil grains and has much to do with accelerat- 
ing granulation. 

Animals also affect soil structure. Earthworms, by 
carrying materials to the surface, exert a mixing effect, 
while the lines of seepage and zones of weakness developed 
through their burrowing proclivities are of no mean im- 
portance. Insects, especially ants and other burrowing 
creatures, aid in this and in other ways. 

1 Fippin, E. O. Some Causes of Soil Granulation. Trans. 
Amer. Soe. Agron., Vol. 2, pp. 106-121. 1910. 



SOIL STRUCTURE 193 

127. Addition of lime. — One of the important effects 
of lime is in its flocculating action. This agglomeration, 
as already explained under colloids, is the drawing to- 
gether of the finer particles of a soil mass into granules. 
When caustic lime is mixed with water containing fine 
particles in suspension, there is almost immediately a 
change in the arrangement of the particles. They appear 
first to draw together in light, fluffy groups, or floc- 
cules, which then rapidly settle to the bottom so that 
the supernatant liquid is left clear or nearly so. This 
phenomenon is termed flocculation, because of the 
groups of particles. It is not an action limited to 
caustic lime alone, however, but because of the useful- 
ness of this compound in other ways, and because of 
its very strong action, it is ordinarily used on soils. 
This flocculating tendency when caustic lime is added 
goes on in the soil as well as with suspensions, although 
more slowly. In general the lime serves to satisfy the 
adsorptive capacity of the colloidal material, and by 
throwing down these colloids develops lines of weakness. 
The cohesive power of the soil is thus localized and 
granulation must necessarily occur. 

The various forms of lime differ in their granulating 
capacities, calcium oxide and calcium hydrate being very 
active while calciiun carbonate is relatively inactive in 
this regard. For this reason, if flocculation effects are 
desired, the oxide or hydrate combinations are added. 
The relative influences of lime on puddled clay as measured 
by penetration is shown in the following table ; ^ the soil 
was dried once and the untreated soil was used as 100 
per cent : — 

' Fippin, E. O. Some Causes of Soil Granulation. Trans. 
Amer. Soc. Agron., Vol. 2, pp. lOG-121. 1910. 



194 SOILS : PROPERTIES AND MANAGEMENT 

Percentage 
of pene- 
tration 

1. Puddled clay 100 

2. Clay plus 2 per cent CaO 56 

3. Clay plus 4 per cent CaO 43 

4. Clay plus 6 per cent CaO 33 

5. Clay plus 5 per cent CaCOs 98 

6. Clay plus 10 per cent CaCOs Ill 

7. Clay plus 25 per cent CaCOs 95 

In the soil the oxide and hydrate revert to the carbonate, 
but before this change occurs the flocculating effects have 
been exerted and the lines of weakness so essential to 
granulative processes have been developed. Lime really 
does not produce granulation in a normal soil through 
its own action alone, but is aided by the other influences 
already discussed. 

Warington ^ reports a statement of an English farmer 
to the effect that by the use of large quantities of lime on 
heavy clay soil he was enabled to plow with two horses 
instead of three. It is generally true that soils rich in 
lime are well granulated, and maintain a much better 
physical condition than soils of the same texture that 
are poor in lime. 

128. Tillage. — The effect of tillage on soil structure 
is to produce lines of cleavage, and these, when produced 
by plowing, are multitudinous and fairly uniformly dis- 
tributed. Plowing, when the moisture content is suit- 
able, tends to break the soil into thin layers, which move 
one over the other like the leaves of a book when the pages 

1 Warington, R. Physical Properties of Soil, p. 33. 
Oxford. 1900. 



SOIL STRUCTURE 195 

are bent. This disturbance of the existing arrangement 
of particles puts in motion the two forces that have al- 
ready been discussed, the pull of the water film and the 
binding power of the colloidal matter. The strength 
of cohesion between small particles, such as clay, can be 
realized when one considers the tenacity with which these 
particles are held together in dried puddled soil. This 
cohesive attraction is inversely proportional to the square 
of the distance between the centers of the attracting bodies. 
Particles that can be brought as closely together as can 
clay particles may be thus held with great firmness. 
The effect of tillage when an excess of water is present 
is to force the particles into large masses and bring about 
a generalized exertion of the forces of plasticity. The 
soil then becomes puddled. Tillage when the soil is 
too dry results either in clodding or in the soil's becom- 
ing so pulverized that it becomes puddled on wetting. 
As already emphasized, proper pulverization by tillage, 
especially by plowing, may occur only when the soil is 
in optimum moisture condition. 

129. The action of the plow. — The plow brings about its 
effects because of the differential stresses set up in the fur- 
row slice as it passes over the share and the moldboard. 
The soil in immediate contact with the plow surface is re- 
tarded by friction, and the layers above tend to slide over 
one another much as the leaves of a book when they are 
bent. If the soil is in just the right condition, maximum 
granulation results ; but if the moisture is too high or too 
low, puddling or clodding may follow, especially on a 
heavy soil. Not only does a shearing occur, but this 
shearing is differential, due to the slope of the share and 
especially to the curve of the moldboard. Where the 
soil is to be turned over with the least expenditure of 



196 SOILS: PROPERTIES AND MANAGEMENT 

force, the share is sloping and is set to deHver a slanting 
cut, and the moldboard is long and gently inclined. This 
allows the furrow slice to be turned with little granulation 
and a minimum expenditure of energy. When maximum 
granulation and pulverization are desired, the moldboard 
is short and sharply turned, and the share is less sloping 
and the cutting edge is less slanting. Such conditions 
make for the development of more friction and the genera- 
tion of those internal twisting and shearing stresses neces- 
sary for good granulation. The sharper the bending of 
the furrow slice, the greater are the internal stresses set 
up. While the plow is the very best pulverizing agent 
when optimum soil moisture conditions prevail, it is also 
a most effective puddling agent when the soil is wet. 
Therefore care in the judging of optimum conditions for 
plowing is a most important feature in the maintenance 
and encouragement of soil granulation and tilth. 

130. Resume. — The factors controlling the struc- 
tural condition of any soil are found to be plasticity and 
cohesion. As these increase, the tendencies of a soil to 
puddle when wet and to clod when dry are augmented. 
Therefore, in heavy soils a decrease in these factors is 
advisable, through a careful control of moisture and a 
bettering of the granular structure of the soil. Granu- 
lation, while due to some extent to the localized influence 
of the water film, is traceable largely to the colloidal 
matter which acts as a binding agent. It is really a 
concentration of the forces of cohesion and plasticity 
around numberless localized foci. Graiuilation takes 
place under the influence of wetting and drying, freezing, 
plants and animals, addition of humus and lime, and 
tillage operations, especially plowing. Due to the high 
cohesion and plasticity of heavy soils, the moisture zone 



SOIL STRUCTURE 197 

for successful plowing is relatively narrow. The ability 
to detect w^hen this zone has been reached in a clay soil 
is one of the essentials of successful soil management. 
Another essential is the effective widening of such a 
zone by granulation operations. The optimum mois- 
ture condition for tillage is also the optimum condition 
for plant growth — a happy coincident, since by regu- 
lating the moisture content for plant development condi- 
tions are rendered most favorable for all soil activities. 
It is thus possible to realize that criterion in all soil physi- 
cal operations, a maximum tilth. 



CHAPTER XI 

THE FORMS OF SOIL WATER AND THEIR 
MOVEMENT 

Under all normal conditions the soil bears a certain 
amount of moisture, which must be reckoned with in 
any study whether of a practical or of a theoretical na- 
ture. Moreover, the amount of water varies in its char- 
acteristics according to its position. It also has move- 
ment, which goes far in determining its usefulness to plants. 
Before a discussion of the different forms of water, their 
movement, and their availability to plants, may be entered 
into, howe^'er, some way of quantitatively stating the 
amounts present must be determined upon. 

131. Methods of expressing soil moistiire. — During 
the many years of soil investigation, especially where the 
problems had to deal either directly or indirectly with 
moisture, five methods of water expression have been 
evolved, their use depending on the nature of the work 
and on the points to be expressed. These may be listed 
under two general heads : — 

A. Percentage expression 

1. Percentage on a wet basis 

2. Percentage on a dry basis 

B. Volume expression 

1. Cubic inches to the cubic foot of soil 

2. Percentage by volume 

3. Surface inches 

198 



THE FORMS OF SOIL WATER 199 

The simplest way of explaining the application of these 
methods for the expression of the amount of water in a 
soil is by a specific case. Suppose a certain soil in field 
condition weighs 100 pounds to a cubic foot and carries 
10 pounds of water. Obviously it would contain 10 
per cent of water by the wet method of calculation, or 
11.1 per cent of water, using the absolutely dry soil as 
a basis. A pound of water contains 27.6 cubic inches; 
therefore the amount of water carried by this soil expressed 
by volume would be 276 cubic inches for every cubic 
foot of soil. The percentage by volume would equal 
(276 -r- 1728) X 100, or 16 per cent. An inch of water 
covering the top of a cubic foot weighs 5.2 pounds. Ob- 
viously the number of surface inches which this 10 pounds 
of water would occupy if placed on the top of the cubic 
foot of soil would be 10 -r- 5.2 or 1.92 surface inches. 

The first method of moisture expression, as percentage 
on a wet basis, is open to two serious objections. In the 
first place, two different percentages of water in different 
samples of the same soil do not represent the same degrees 
of wetness as are expressed by the percentages. For 
example, 100 grams of wet soil containing 5 per cent of 
water would consist of 5 grams of water and 95 grams of 
soil, a ratio of 1 to 19. If the soil contained instead 25 
per cent of water, the ratio would be 1-3 instead of 1-3.8, 
as the ratio of the percentages would naturally lead one 
to expect. The second objection is just as serious and 
arises from the fact that soils have different apparent 
weights. For example, 5 per cent of water on the wet 
basis for a clay weighing when dry 70 pounds to the cubic 
foot would equal 3.72 pounds, while 5 per cent on a sand 
weighing 100 pounds would give 5.25 pounds of the same 
volume. The error of such a method of expression is 



200 SOILS: PROPERTIES AND MANAGEMENT 

obvious, not only in comparing the water content of the 
same soil, but in comparing different soils as well. 

In using a percentage of moisture based on the dry 
soil instead of on the wet, the first of the above objections 
is eliminated. Consequently this method of expression 
is perfectly legitimate as long as soils having about the 
same apparent specific gravity are compared. As soon 
as soils of different weights are considered, however, a 
more nearly accurate method must be employed. Ob- 
viously, then, the only really rational mode of moisture 
statement is by the volume method. In ordinary calcu- 
lations of water, however, the percentage by dry weight 
is generally used because of its simplicity and the facility 
of expression that it affords. It is also much easier to 
establish than a percentage based on volume. 

The first and second methods of volume expression are 
of about equal value as far as direct comparison goes. For 
the actual water present the nmnber of cubic inches to a 
cubic foot of soil is perhaps preferable, as it shows the exact 
amount of water contained and may easily be converted 
to pounds to a cubic foot or tons to an acre as the case 
may be. The third volume statement is generally used in 
field practice, especially in irrigated regions, where water 
is measured in inches in depth to an acre of area. Such 
a statement of the available water in a soil not only is 
convenient, but also gives a direct comparison with the 
probable rainfall of the growing season. 

132. Kinds of water in the soil. — As has already been 
demonstrated, a soil of a definite volume weight has a 
definite pore space which may be occupied by air or by 
water, or shared by both, as the case may be. Of course, 
an ideal soil for plant growth is one in \\hic'h there is 
both air and water, the proportions depending on the 



THE FORMS OF SOIL WATER 201 

texture and the structure of the soil and the character 
of the crop. Assuming for the time being, however, that 
the pore space is entirely filled with water, or, in other 
words, that the soil is saturated, three forms of water 
are found to be present — hygroscopic, capillary, and 
free, or gravitational. These forms differ, not in their 
composition, but in the position that they occupy in rela- 
tion to the soil particles. 

The hygroscopic and capillary water are both film 
forms ; that is, they surround the soil particle, being held 
partly by the attraction of the particle and partly by the 
molecular attraction of the liquid for itself. The hygro- 
scopic film is very thin, being water of condensation, or 
adsorption. When this film is satisfied and moisture is 
still present, the capillary water film begins to form. The 
line of demarcation between hygroscopic and capillary 
water is not sharp. The general difference between the 
two forms may be considered as being not only one of 
position, but also one of movement, this power being pos- 
sessed only by the capillary film. With a change in any 
controlling condition, such as temperature, hygroscopic 
water may change to capillary, or capillary water to 
hygroscopic, as the case may be. As the capillary water 
continues to increase and the film becomes thicker and 
thicker, a point is at last reached at which gravity over- 
comes the surface tension of the liquid and drops of water 
form which tend to move downward through the air 
spaces, being now subject to movement by the attrac- 
tion of gravity. Free, or gravitational, water then also 
becomes present in the soil. If water is still added, the 
gravitational water continues to increase until the air 
is almost entirely displaced and a saturated condition 
results. There may be a change of capillary to free water 



202 SOILS: PROPERTIES AND MANAGEMENT 

or of free water to capillary with a change of structure, 
temperature, or pressure, as was seen to be the case be- 
tween the hygroscopic and capillary moisture. The forms 
of water present in a saturated soil may be conveniently 
represented by the following diagram : — 

HYGROSCOPIC I TAPILLARY | FREE 

Fig. 30. — Diagram representing the three forms of water that may 
be present in a soil. 

133. Hygroscopic water. — The hygroscopic water 
in a soil has been spoken of as the water of condensation, 
or adsorption. It is, however, quite distinct from water 
condensed on a surface colder than the atmosphere in 
which it is placed. All bodies possess the power, to 
a greater or less degree, of adsorbing water even when 
at the same temperature as the air with which they are 
in contact, provided, of course, that the air contains water 
vapor. The hygroscopic film may be continuous or only 
partly continuous, depending on the condition of the 
surface. In fact, the movement of water over surfaces 
is often greatly facilitated by an already existing hygro- 
scopic film. External conditions being constant, the 
amount of hygroscopic water of A-arious materials is 
determined by two factors: (1) the characteristics of the 
material itself, and (2) the amount of surface it exposes. 

It is a well-known fact that various materials differ 
in the amount of hygroscopic water they will hold, due 
to the attraction of the substances themselves for water. 
The differences in the thickness of the film is so slightly 
altered, however, by differences in materials, that, other 
factors being constant, the hygroscopic water becomes 
a function almost entirely of surface. Glass becomes 



THE FORMS OF SOIL WATER 



203 



far more hygroscopic when pulverized. Porous bodies 
are especially high in hygroscopic water, sometimes 
holding as much as 20 to 30 per cent of moisture. The 
following data, drawn from Ammon ^ and von Dobeneck,^ 
although no doubt faulty, illustrate the differences in 
hygroscopicity of materials commonly found in soils 
and make plain the complexity of the question when 
applied to soil phases : — 

Percentage of Hygroscopicity of Different Substances 
AT 20° C. WHEN Exposed for One Day to Saturated 
Air 





Ammon 


Von Dobeneck 


Humus 


1.5.96 


18.04 


Ferric oxide 


19.76 


20.41 


Kaolin 


.47 


3.55 


Limestone 


.29 


.32 


Quartz 


.07 


.17 



One of the characteristics peculiar to colloids in partic- 
ular is a high adsorptive power for moisture, this giving 
them properties not usually possessed by crystalloids. 
Gelatinous precipitates of silica, ferric oxide, and alumin- 
ium oxide are good examples. Colloidal humus, gela- 
tin, and agar are noted for their adsorptive powers. The 
water in such cases is not simply adsorbed on the external 



1 Ammon, Georg. Untersuchungen iiber das Condensa- 
tionsvermogen der Bodenconstituenten fur Gase. Forseh. 
a. d. Gebiete d. Agri.-Physik, Band II, Seite 1-46. 1879. 

- Dobeneck, A. F. von. Untersuchungen iiber das Absorp- 
tionsvermogen und die Hj'groskopizitjit der Bodenkonstitu- 
enten. Forseh. a. d. Gebiete d. Agri.-Physik, Band XV, 
Seite 163-228. 1892. 



204 SOILS: PROPERTIES AND MANAGEMENT 

expanses, but is distributed over the great internal sur- 
face exposure. Such water cannot be expelled by ordi- 
nary drying, but the material must be subjected to a high 
heat in order to drive oflP even a part of the water so held. 
The question is greatly complicated also by the fact that 
some bodies have a chemical affinity for water. This 
results in the formation of hydrates and other salts. Such 
water cannot be expelled without the breaking-up of the 
compounds. 

Ordinary soil possesses to an extraordinary degree 
the three characteristics already cited : that is, it exposes 
a very large amount of free surface ; it tends to generate 
continuously large amounts of colloidal material such as 
ferric hydrate, aluminium hydrate, silicic acid, and espe- 
cially humic materials in a colloidal state ; and it always 
has present compounds having an affinity for water. 
However, since these compounds are easily satisfied, and 
also since the adsorptive power of colloids is due to the 
surface exposed, it may be considered that, other condi- 
tions being equal, the hygroscopicity of the soil is essen- 
tially a surface phenomenon. Although for all practical 
purposes hygroscopicity may be considered as having 
special relation to surface, exact correlation is not easy 
partly because of the difficulty of accurately determining 
the surface exposed by a normal soil. 

134. Effect of texture and humus on hygroscopicity. — 
The question being thus reduced to a surface consideration, 
it is evident that the texture of the soil, external factors 
being under control, is the determining factor. The fol- 
lowing figures from Loughridge,^ by whom the hygroscopic 

1 Loughridge, R. H. Investigations in Soil Physics. 
California Agri. Exp. Sta., Rept. of Work of the Agri. Exp. 
Stations of California for 1892-3-4, pp. 7G-77. 



THE FORMS OF SOIL WATER 



205 



moisture was determined by exposing the air-dry soil at 
15° C. to a saturated atmosphere and then drying at 200° 
C, illustrate this point : — 

Hygroscopic Capacity of Various Soils 



Soils 



Per cent Clay 
Material Remain- 
ing IN Suspension 

AFTER Standing 
FOR 24 Hours 



Hygroscopic 

Water Expressed 

in Percentage 



15 clays . . 
7 clay loams 
9 loams . 
4 sandy loams 
4 sands . 



31.97 

17.15 

12.06 

7.39 

2.93 



10.45 
6.06 
5.18 
2.50 
2.21 



Apparently, the finer the soil, the greater is the hygro- 
scopicity. The finer the soil, the higher also is the per- 
centage of clay, and consequently the greater is the amount 
of material likely to be present in a colloidal state. As a 
matter of fact, the hygroscopic moisture as shown above 
is roughly proportional to the clay ; and as clay, espe- 
cially the finer forms, is largely colloidal in nature, the 
colloidal content of a soil practically determines the hygro- 
scopic content. This fact is the basis for INIitscherlich's ^ 
method of colloid estimation, in which hygroscopic mois- 
ture determined under certain controlled conditions is 
used as a relative measure of colloidal content. The vari- 
ous grades of particles constituting the textural make-up 
of a soil, then, do not possess the same weight in the deter- 
mination of hygroscopicity, the dominant grade being 
clay, especially that part which has, by either physical 



I Mitscherlich, E. A. This text, paragraph 111. 



206 SOILS: PROPERTIES AND MANAGEMENT 

or chemical means or both, been thrown into a colloidal 
condition. Especially do the humous colloids, as has 
already been shown, function in this regard, so that the 
organic matter must be of verj^ great importance in deter- 
mining the hygroscopic capacity of any soil. The finer 
the soil, the greater is the amount of hygroscopic water 
merely because of the large area of surface exposed. 
Also, any practice that will increase the colloidal material 
— the humous colloids being very susceptible to increase 
by proper soil management — the higher will be the per- 
centage of this hygroscopic moisture. Texture and humus, 
then, govern the hygrosc()})icity of most soils. 

135. Nature of the film. — The nature of this thin film 
which is designated as hygroscopic water has not as yet 
been determined. Held so strongly by a molecular force 
averaging probably 10,000 atmospheres, generated by 
adhesion and cohesion, it is not definitely known whether 
the film exists as a liquid or a vapor. Consequently it 
cannot be expected to conform to the laws that are gen- 
erally found to apply to capillary films. In many cases 
the film may not be continuous, and being so very, very 
thin, it may even possess a negative surface tension. The 
radius of influence of a particle in water has been shown 
by Chamberlain ^ to be about 1.5 X 10~^ centimeters. 
Within this zone the molecules of water are much restricted 
in their motions. The thickness of the hygroscopic film on 
quartz particles as calculated by Briggs " is 2.()() X 10~^ 
centimeters, showing that the outer edge of the hygroscopic 

1 Chamberlain, C. W. The Radius of Molecular Attrac- 
tion. Physical Review, Vol. 31, pp. 170-182. 1910. 

- Briggs, L. J. On the Adsorption of Water Vapor and of 
Certain Salts in Aqueous vSolution by Quartz. Jour. Phys. 
Chem., Vol. 9, pp. 017-641. 1905. 



THE FORMS OF SOIL WATER 



207 



film, where the Avater to a large extent loses its movement, 
is considerably without this zone of influence. In order 
to give some idea of the extreme minuteness of the hygro- 
scopic film, it may be said that its thickness is less than 
the diameter of the smallest known soil bacteria. In 
moving from the surface of a particle outward through 
an ordinary Avater film, passage is first made through the 
zone of influence. When the edge of this is reached, an 
area is passed through which continues Avith constantly 
increasing capacity for molecular motion until the outer 
edge of the hygroscopic film is crossed, Avhere molecular 
activity reaches its maximum. 

136. Effect of humidity and temperature on hygro- 
scopic water. — Two external conditions seem to affect 
the amounts of hygroscopic Avater that a soil may hold 
under definite conditions — humidity and temperature. 
As a general rule, the higher the humidity, the higher is 
the hygroscopic moisture. The experiments of A'on Dobe- 
neck ^ Avith quartz and humus illustrate this point : — 

Percentage of Hagroscopic Water held at Various Humid- 
ities AFTER AN EXPOSURE OF TwENTY-FOUR HoURS AT 

20° C. 



Quartz 
Humus 



30 
Per cent 

.04.5 
4.055 



50 
Per cent 

.053 
7.765 



70 
Per cent 

.076 
10.589 



90 
Per cent 

.119 
15.676 



100 
Per cent 

.175 
18.014 



The results as to the effects of a rise in temperature 
on the hygroscopic film are not so definite. Most in- 



' Dobeneck, A. F. von. Untersuehungen iiber das Absorp- 
tionsvermdgen und die Hygroskopizitat der Bodenkonstitu- 
enten. Forsch. a. d. Gebiete d. Agri.-Physik, Band XV, Seite 
163-228. 1892. 



208 SOILS: PROPERTIES AND MANAGEMENT 

vestigators ^ find that as the temperature is increased 
the hygroscopicity becomes lowered, thus following the 
general laws of adsorption. Ililgard, however, obtained 
opposite results when the air was saturated, although his 
data agreed with previous results when hygroscopicity 
was studied in an atmos])here luisatisfied as to its capac- 
ity for water vapor. King ^ explains this discrepancy 
as being due to the very high vapor pressure generated 
by a saturated atmosphere at high temperatures, causing 
a more rapid taking-up of water by the soil than was 
lost from its surface. The time necessary for a soil to 
assume its maximum thickness of adsorbed water is un- 
certain. Hilgard ^ used seven hours in his determina- 
tions, while Mitscherlich ^ exposed his soil for several 
days. A soil continues to increase in weight slowly as 
its time of exposure to moist air is increased, so that a 
sharp line of demarcation between capillary and hygro- 
scopic water is difficult to establish. Capillary water 
may even be present in the minute interstices before the 
hygroscopic film is elsewhere satisfied.^ 

137. Determination of hygroscopicity. ^ The method 
of the determination of the nuixinium hygroscopicity of a 
soil, or, in other words, the hygroscopic coefficient, is 
simple in outline. The soil, in a thin layer, is exj^osed 



1 Patten, H. E., and Gallagher, F. E. Adsorption of Vapors 
and Gases by Soils. U. S. D. A., Bur. Soils, Bui. 51, p. 33. 
1908. 

2 King, F. H. Physics of Agriculture, pp. 179-180. 
Published by the author, Madison, Wisconsin, 1910. 

' Hilgard, E. W. Soils, pp. 190-201. New York. 1911. 

'' Mitscherlich, E. A. Bodenkunde, pp. 5G-58. Paul 
Parey, Berlin. 1905. 

* Briggs, Ij. J. The Mechanics of Soil Moisture. U. S. 
D. A., Bur. Soils, Bui. 10, p. 12. 1897. 



TUE FORMS OF SOIL WATER 209 

to an atmosphere of definite humidity under conditions 
of constant temperature and pressure. CompHqations 
arise from the necessity of using a very thin layer of soil, 
from the difficulty of controlling humidity, and from the 
tendency of capillary water to form in the soil interstices 
before the hygroscopic film is satisfied. The question of 
how long the exposure should take place is a very serious 
factor, as has already been pointed out. In the drying 
of the soil after exposure a vexing condition also is en- 
countered, in that as the temperature is raised, the giving- 
off of water vapor continues. It is evident, therefore, 
that not only must any method be more or less arbitrary, 
but that its value can be only comparative. The method 
of Mitscherlich, as already described,^ is probably the 
most nearly accurate. lie exposes the dry soil under 
partial vacuum over 10 per cent sulfuric acid and water. 
The partial vacuum is to hasten adsorption, and the acid 
to prevent a fully saturated air, thereby cutting down 
chances of dew deposition. 

138. Heat of condensation. — The amount of energy 
necessary to expel the hygroscopic film from around a 
soil particle is very great, since its only movement is 
thermal. As a matter of fact, it is really impossible to 
divest the soil grain entirely without causing the loss of 
moisture other than that simply adsorbed. As so much 
energ\' is expended in removing this film, it is reasonable 
to expect that a certain amount of heat of condensation 
when the film is resumed would become apparent. Pat- 
ten ^ offers the following quantitative data concerning 
this point : — 

1 Mitscherlich, A. E. This text, paragraph 111. 

2 Patten, H. E. Heat Transference in Soils. U. S. D. A., 
Bur. Soils, Bui. 59, p. 34. 1909. 



210 SOILS: PROPERTIES AND MANAGEMENT 

Heat Evolved by Wetting Soils Dkied at 110° C. 



Soil 


Calories per 
Kilo of Dry Soil 


Coarse quartz 


150 


Podunk fine sandy loam 

Norfolk sand 


200 

347 


Hagerstown loam 


1108 




3785 


Muck soil (25 per cent organic matter) . . . 


6413 




139. Capillary water. — It has been shown in the pre- 
vious discussion that a hirge proportion of the hygroscopic 
film is beyond the radius of influence of the particle and 
is not held so rigidly as is the inner portion. In other 
words, in this film a certain amount of molecular move- 
ment is possible, this movement depending on the dis- 
tance from the particle. As soon, how- 
ever, as the boundary of the hygroscopic 
film is crossed, a comparatively thick 
,, „ ^. film of moisture is reached in which 

I<iG. .31. — Diagram . r xu 

showing the roia- molccular movement, except ror the 
tionship of the influence of viscositv, is perfectly free 

hygroseopic and . i i m/ x ' / 

capillary water and ununpedcd. 1 hese two zones (see 
films surrounding ]?i<^ 31) — ouc in which caiMllarN' move- 

a soil particle. ' . i i> i ' 

(s), particle; ment IS more or less tree, and a com- 
(i), zone of infiu- parativclv thin film in which molecular 

ence of particle ; ' ' . • i i 

(ir), outer edge of movement becomes increasnigly slug- 
hygroscopic zone ; „ig]^ as the radius of influence of the 

(c), capillary film. ^ ., . . , , ^, 

soil gram is approached — are there- 
fore clearly dift'ercntiated. The capillary water dift'ers 
from the hygroscopic moisture (l) in that it is largely in 
a liquid state and consequently is governed by the ordi- 
miry laws of liquids ; (2) in that it evaporates at ordinary 



THE FORMS OF SOIL WATER 211 

temperatures, being held with less tenacity ; and (3) in 
that it has the power of movement from place to place 
within the film, hence the name capillary water. 

140. Surface tension and the force developed thereby. 
— The power that tends to hold this capillary water in 
place against the force of gravity, a constant, depends 
on the surface tension of the liquid. This phenomenon 
of surface tension is due to the existence of certain molec- 
ular forces acting from within. In a drop of water, for 
example, the particles are attracted equally in all direc- 
tions and consequently are able to move with perfect 
freedom. The molecules on the surface of the drop, 
however, are not in such an equilibrium of attraction, 
since the pull of the water particles within is greater than 
that of the air particles without. The resultant attrac- 
tion is therefore inward, and is directed along a line per- 
pendicular to the surface at that point. The result is 
the de\'elopment of a more or less ideal membrane, the 
effective force of which is not affected by the amount of 
the surface, but l)y the curvature. In a sphere the force 
or pressure developed by surface tension is equal to twice 
the surface tension divided by the radius. This increase 
of the effective force by curvature of film is very impor- 
tant as regards soil water, since, as will be shown later, it 
governs the movement of ca])illary water from one particle 
to another, the direction of the movement being deter- 
mined by a difference in pressure as developed by un- 
equal curvatures of film surfaces. 

As a result of this force developed by surface tension, 
the water film around a soil particle tends to equalize 
itself until this pressure is everywhere the same. On 
this force depends also the thickness of the capillary film. 
Under any given condition this capillary fihii will con- 



212 SOILS: PROPERTIES AND MANAGEMENT 



tinue to thicken until the mass of the water is so great 
as to allow gravity to come into play and pull enough 
water away to again restore the equilibrium. The soil 
particle would at this point be maintaining its maximum 
thickness of caj)illary film. It is also quite evident that 
as the capillary film is thinned — as, for example, by 
evaporation — the force developed by surface tension 
would be increased, due to increased curvature of the 
film, and the difficulty of removing the external layers 
of the film would naturally become greater. 

141. The form of water surfaces between soil particles. 
— In the case of a soil, however, the question of the 
capillary film becomes more complex, since a great num- 
ber of different-sized particles are present in more or less 
close contact with one another. This means that under 
normal soil conditions the capillary film is continuous 
from one particle to another — a very different question 
to consider from that of a film about a single isolated soil 

grain more or less 
spherical in shape. 
Suppose, for example, 
that two particles, 
each carrying a capil- 
lary water film, be 
brought into such 
contact that the films 
coalesce. There are 
now two distinct sur- 
faces — that at A, A' (see Fig. 32), with the curvature 
of the original film, and that at B, which is very acute 
and which naturally must exert a very great outward 
pull. Under the stress of this {)ull developed by the 
surface tension acting in this film of very great curvature, 





Fig. 32. — Diagram showius tlio coalosconce 
and readjustment to the capillary film of 
two soil particles when brought in con- 
tact. At left is shown the condition be- 
fore adjustment with a sharp angle at B ; 
at right the films arc shown in equi- 
librium with a great thickening at li. 



THE FORMS OF SOIL WATER 213 

the water is drawn into the space between the particles, 
where it becomes thicker than the capillary film about 
the particles. This readjustment continues until the 
forces developed by the two films become equal. An 
equilibrium is now established. It is evident, then, that 
as the capillary water becomes less in a soil from any 
cause, the moisture collected in the spaces between the 
particles becomes less and less, but still remains thicker 
than the films about the particles themselves. What 
percentage of the capillary water is held in the thickened 
waists of the soil grains cannot be calculated, but it is 
probable that this moisture makes up the major part 
of the capillary water of any soil. One of the errors 
in the determination of the hygroscopic coefficient of a 
soil, as already pointed out, arises from the tendency 
toward the formation of capillary water in these angles 
between the soil particles before the hygroscopic film on 
the grains themselves becomes satisfied. 

142. Factors affecting amount of capillary water. — 
As might naturally be expected, the factors that tend to 
vary the amount of capillary water in a soil are several, 
and their study is more or less complex, due to the second- 
ary influences that they may generate. These factors 
may be discussed under four heads: (1) surface tension, 
(2) texture, (3) structure, and (4) organic matter. 

143. Surface tension and the amount of capillary 
water. — Any condition that will influence surface ten- 
sion will obviously influence the thickness of the capillary 
film, because of a variation in the forces thereby de- 
veloped. A rise in temperature, by lowering the surface 
tension, would consequently lower the capillary capacity 
of the soil, and if the soil were capillarily saturated would 
allow some of the water to become gravitational in its 



214 SOILS: PROPERTIES AND MANAGEMENT 

nature. A lowering of the temj)erature would cause a 
change in the opposite direction. This theory has been 
verified by certain experiments by King/ in which he 
found, other conditions being constant, a very decided 
influence on capillary water through change of tempera- 
ture. Wollny ^ has shown that a depression of from .05 
per cent in sand to as high as 3.7 per cent in kaolin may 
occur from a rise in temperature of twenty degrees. The 
surface tension of a liquid may also be greatly changed 
by the addition of salts, and, since the soil always carries 
some material in solution, the surface tension, and conse- 
quently the capillary capacity, might be expected to 
increase. As a matter of fact, the soil solution is very 
dilute, and even if large amounts of fertilizer salts were 
added the adsorptive power of the soil would tend to 
maintain a very dilute soil water at the surface of the 
films. Again, as humus decay is continuously going on, 
oily materials are probably produced which would tend 
to spread over the capillary films and greatly reduce their 
surface tension. Therefore, as far as is now known of the 
two varying influences, temperature change is by far the 
most potent in its influence on capillary capacity. 

144. Texture and the amount of capillary water. — 
The finer the texture of a soil, the greater is the number 
of angles between the particles in which a film of capillary 
water may be held ; also, the actual amount of surface 
exposed by the particles is immensely larger than in a 



1 King, F. H. Fluctuations in the Level and Rate of Move- 
ment of Ground Water. U. S. D. A., Weather Bur., Bui. 5, 
pp. 59-61. 1892. 

= Wollny, E. Untersuchungen iiber die Wasserkopacitiit der 
Bodenarten. Forseh. a. d. Ge])iele der Agri.-Physik, Band 9, 
Seito 361-378. 1886. 



THE FORMS OF SOIL IVATER 



215 



coarse soil. Due to these two conditions, a soil of fine 
texture will contain considerably more capillary water 
than one of which the texture is coarse. The maximum 
capillary capacity of a soil is not directly proportional to 
the surface, as was roughly proved to be the case with 
the hygroscopic coefficient. This is probably because 
the angle exposures between the grains increase in number 
as the texture becomes finer much faster than the actual 
surfaces developed by the particles are generated. The 
capillary water in any soil varies with the height of the 
column. This comes about from the gravity effects 
on the liquid surrounding the particle. If the liquid had 
no weight, gravity would not be a factor and the same 
thickness of film would be found at 
any point in a soil column. Such a 
condition would greatly simplify the 
study of soil moisture. If a number of 
particles (see Fig. 33) carrying maxi- 
mum capillary films are brought together 
vertically, the weight of the whole con- 
ducting film is thrown momentarily on 
the ca])illary surfaces at the top. The 
capillary sjjaces at this point immediately 
lose water downward, so that they may 
assume a greater curvature and thus 
support this extra weight thrown on 
them. This curvature must be sufficient 
to balance the curvature pressure of the 
particles below plus the weight of the 
water in the connecting films. The par- 
ticles beneath are at the same time un- 
dergoing a similar adjustment with a set of jjarticles still 
farther below, losing water in order to allow a change of 



Fig. 33. — Diagram 
showing the ad- 
justment of the 
capillary film in a 
long column and 
the appearance of 
free or gravita- 
tional water if the 
weight is too 
great for the sup- 
porting films. 



216 SOILS: PROPERTIES AND MANAGEMENT 



curvature. A thinning of these films results, but not to 
such an extent as in the particles above. The action 
continues in this manner through each capillary surface 
until equilibrium is established, the change in thickness 
of film being less and less in each case due to the cumu- 
lative support of the films above. If the amount of 
capillary water present is too great to be supported by 
the films, enough is lost by gravity at the bottom to 
bring about an equilibrium. The film is at its maximum 
at the bottom of the column, but decreases in thickness 
as the column is ascended, not only on the particles 
themselves, but in the angle interstices as well. This is 
necessary, as each successive film must support an in- 
creased weight of water. It is, therefore, evident that 
it is impossible to assign any definite figure as to the 
capillary water capacity of a soil. Only relative or 
comparative data may be quoted. The following diagram 



^ 


■4^ \ 




CL/tY 










Hi 


JO \ 




SArfOY ■•. 












\ 
\ 
\ 


, 


±OAM 
















SAno 


^.. 




















% 








r / 


o / 


f 2 


2 


S 3 


OC/otVATd 



Fig. 34. — Diagram showing the distribution of moisture in capillary 
columns of soil of different textures. The end of each soil column 
rests in free water. 



THE FORMS OF SOIL WATER 217 

(see Fig. 34) from Buckingham ^ makes clear not only 
the influence of texture on capillary water, hut also the 
distribution of water in a capillary column. 

The final mean water content of these soils was 10, 
15, and 20 per cent, respectively, for the fine sand, the 
sandy loam, and the clay ; showing that as the texture 
becomes finer, the greater is the average capillary content 
even after allowing for the differences in hygroscopic 
moisture. 

145. Effect of structure on the amount of capillary 
moisture. — The structure of the soil, or, in other words, 
the arrangement of the particles, will become a factor in 
capillary capacity in so far as it affects the amount of 
effective capillary surface. _ Any arrangement of parti- 
cles that will increase the number of angles of contact will 
evidently increase the amount of capillary water. The 
compacting of a loose soil will increase the possible capil- 
lary moisture until all the interstitial space becomes 
capillary in its nature ; further compacting will then 
cause a marked decrease. The granulation of a clay soil, 
by producing a criunb structure and by actually increas- 
ing the effective surface exposure, tends to increase its 
water-holding capacity. At the same time the compacting 
of a sand, by increasing not only the actual effective sur- 
face, but also the number of angles possible for capillary 
concentration, will cause a rise in the capillary capacity 
of that soil. 

In a study of this kind it is very evident that the aver- 
age data of a long column should be considered, since 
the percentage of moisture at any one point is not in- 
dicative of the true capillary capacity of a soil. Such 

1 Buckingham, E. Studies on the Movement of Soil 
Moisture. U. S. D. A., Bur. Soils, Bui. 38, p. 32. 1907. 



218 SOILS : PROPERTIES AND MANAGEMENT 

figures have been obtained by Buckingham ' in his study of 
loose and compact soils. The following curves repre- 
sent the general trend of his results : — 





30 X 


VN. 






1 

\ 
\ 




^ 

? 


2a 


L 








\ 




§ 


w 




^^~=^ 


^ 


r^^^ 


\ 


\ 


^ 









^ 


I:^ 


^v~ 


•^ ^ 




s 


/ 





/ 


S 2 


o 


2S 


JO ^o t^Ar£a 



Fig. 35. — Diagram showing the effect of a compaotion upon the distri- 
bution of moisture in capillary columns. (L), loose sandy loam; 
(Z/'), compact sandy loam ; (C), compact clay ; (CO, loose clay. 



While it is e\ident that the mean water content of the 
compact sandy loam is greater than that of the less com- 
pact, the latter showed a higher percentage of moisture 
up to about the tenth inch. The clay shows a more 
marked effect from compacting, dropping in the compact 
sample almost as low^ as the sand, on the average, and 
showing at about ten inches from the end of the colimin 
a percentage of moisture considerably below that of either 
the loose or the compact sand. It is obvious that the 
farmer may do much in the control of capillary water by 
promoting a proper ])iiysical condition of his soil. 

146. Organic matter and the amount of capillary mois- 
ture. — Organic matter, especially when it has been 
reduced to the form of humus, has great capillary capac- 
ity, far excelling in this regard the mineral constituents of 
the soil. Its porosity affords an enormous internal sur- 

1 Buckingham, E. Studies on the Movement of Soil Mois- 
ture. U. S. D. A., Bur. Soils, Bui. 38, pp. 34-35. 1907. 



THE FORMS OF SOIL WATER 219 

face, while its colloids exert an affinity for moisture which 
raises its water capacity to a very high degree. Its ten- 
dency to swell on wetting is but a change in condition 
incident to an approach to its maximum moisture con- 
tent. The following data, taken from a compilation by 
Storer/ give an idea of the capillary capacity of the soil 
organic matter : — 

Percentage 
of water 

1. Humous extract from peat . . . . . . 1200 

2. Non-acid extract from peat 645 

3. Vegetable mold 309 

4. Peat 190 

5. Garden loam, 7 per cent humus .... 96 

6. Illinois prairie soil 57 

7. Field loam, 3.4 per cent humus .... 52 

8. Mountain valley loam, 1.2 per cent humus . 47 

Even after allowance has been made for the increased 
hygroscopic coefficient incident to an increase in organic 
matter, the effect of the latter is very strongly evident 
on the capillary capacity of a soil. Besides this direct 
effect, organic matter exerts a stimulus toward better 
granulation, a condition in itself favorable to increased 
water-holding ])ower. 

147. Determination of capillary water. — The capillary 
water in a sample of field soil may be determined by mak- 
ing a moisture test in the ordinary way for the total water 
contained. This represents the hygroscopic plus the 
capillary water. A determination of the hygroscopic 
coefficient on another sample yields a figure which when 

' Storer, F. H. Agriculture, Vol. I, p. 106. New York. 
1910. 



220 SOILS: PROPERTIES AND MANAGEMENT 

subtracted from the total water will give the capillary 
water present in the sample. The capillary water at 
various points in a soil column may be obtained by sub- 
tracting the hygroscopic coefficient from the various 
percentages of moisture present, since the thin hygroscopic 
film is not influenced by height of column or ordinary 
structural conditions. In ordinary soils, however, the 
differences in hygroscopicity are not so great but that 
the total water retained in a soil column against gravity 
serves as a very good measure of relative capillary 
capacity. 

148. The moisture equivalent of soils. — Briggs and 
McLane ^ have perfected a method of comparing soils 
on the basis of their capacity to hold water against a 
definite and constant centrifugal force of one to three 
thousand times the force of gravity. The soils, in thin 
layer, are placed in perforated brass cups which fit into 
a centrifugal machine capable of developing the above 
force, and are whirled until equilibrium is reached. The 
resultant moisture percentage is designated as the mois- 
ture equivalent. It really represents the capillary 
capacity of a soil of minimum column length when 
subject to a constant and known force or pull. The 
finer the soil, the greater of course is the moisture 
equivalent. The authors also found that 1 per cent of 
clay or organic matter represented a retentive power of 
about .02 per cent, while 1 per cent of silt corresponded 
to a retention of .13 per cent. Representative data 
which show the correlation of the moisture equivalent 
to the textural properties of the various types are given 
in the table on the following page. 

' Briggs, L. J., and McLane, J. W. The Moisture Equiv- 
alents of Soils. U. S. D. A., Bur. Soils, Bui. 45. 1907. 



THE FORMS OF SOIL WATER 



221 



Soil 


Per- 
cent- 
age OP 

Or- 
ganic 
Matter 


Per- 
cent- 
age 

OP 

Sands 


Per- 
centage 
OF Silt 


Per- 
centage 

OF 

Clay 


Mois- 
ture 
Equiva- 
lent 


1. Norfolk coarse sand . 


.9 


87.9 


7.3 


4.8 


4.6 


2. Norfolk fine sandy loam 


1.3 


73.4 


18.1 


8.5 


6.8 


3. Yazoo loam .... 


1.3 


25.8 


G4.1 


10.1 


18.9 


4. Waverlv silt laom . 


2.0 


14.9 


62.9 


22.2 


24.4 


5. Houston clay loam 


3.7 


30.9 


42.5 


26.6 


32.4 


6. Houston clay 


1.4 


10.0 


56.6 


33.4 


38.2 



149. The maximum retentive power of a soil. — xA.n- 
other determination has been devised by Hilgard ^ and 
used to considerable extent by other investigators.^ It 
is designated as the maximum retentive power of a soil. 
A small perforated brass cup is used, having a diameter 
of about 5 centimeters and capable of containing a soil 
column 1 centimeter in height. A short column is used, 
since it is only under such conditions that a soil may re- 
tain against gravity the greatest amount of water. Also, 
the soil is able to expand or contract, as the case may be, 
on the assumption of water until an equilibrium is reached. 
A filter-paper disk is placed in the metal cup, and the soil 
is poured in, gently jarred down, and stroked off level 
with the top of the cup. The cup is then set in water 
and the soil is allowed to take up its maximum moisture. 
After draining, the weight of the wet soil plus the cup, 
together with the weights previously obtained, will allow 
the calculation of the total water contained by the soil. 

150. Capillary movement. — It has already been shown 
how different thicknesses of films on two particles tend 

1 Hilgard, E. H. Soils, p. 209. New York. 1911. 
^ This text, paragraph 181. 



222 SOILS: PROPERTIES AND MANAGEMENT 




Fig. 36. — Diagram show- 
ing the mechanics of the 
capillary movement of 
water in soil. The read- 
justment takes place in 
the direction of (A) due 
to the high tension devel- 
oped by the sharp film 
curvature at this point. 



to become equal, due to the pulling force developed by 
the angle of curvature between the particles. It is evi- 
dent that differences in curvature must be the motive 
force in the capillary movement 
of soil water. Let it be supposed, 
for convenience, that three equal 
spheres when brought in contact 
contain unequal amounts of water 
in the angles of curvature (see 
Fig. 3G). In this case the greater 
pull would exist at A, since the 
angle here is more acute. Conse- 
quently water must move through 
the connecting film until the pull 
at A and that at B become the same. Such an adjust- 
ment might go on o\er a large number of films, and if 
one end of the column was exposed to an evaporation 
of just the right rate and the other end was in contact 
with plenty of moisture, large quantities of water would 
be pumped by capillarity. 

This capillary movement may go on in any direction in 
the soil, since it is largely independent of gravity ; yet 
under natural field conditions the adjustment tends to 
take place very largely in a vertical direction. When 
a soil is exposed to evaporation the surface films are 
thinned and water moves upward to adjust the ten- 
sion. This explains why such large quantities of soil 
water may be lost so rapidly from an exposed soil. 
Capillary adjustment may go on downward, also, as is 
the case after a shower. Here the rapidity of the ad- 
justment is aided by the weight and movement of the 
water of {)erc()lation. 

The capillary adjustment in a soil may go on under 



THE FORMS OF SOIL WATER 223 

two conditions: (1) if the soil c-olmnn is in contact with 
free water ; and (2) if no gravity water is present, the 
movement being merely from a moist soil to a drier one, 
an inexhaustible supply of water not being present. In 
the first case the lower portion of the soil is entirely 
saturated for a short distance above the free water sur- 
face, due to the functioning of the pore spaces as true 
capillary tubes ; above this the film movement becomes 
dominant. The second condition of capillary adjustment 
is the one most commonly found in a normal soil, since a 
water table a short distance below the surface is not 
usually conducive to the best crop growth. In studying 
the rate and height of capillary rise in any soil, however, 
the maintenance of a supply of free water at the lower end 
of the column is usually provided for, since this allows a 
near approach to the maximum capillary capacity for any 
point in the column. 

151. Factors affecting rate and height of capillary 
movement. — To persons familiar with the habits of grow- 
ing plants it is evident that capillary movement must 
play an important part in their nutrition, since the root- 
lets are unable to bring their absorptive surfaces in con- 
tact with all the interstitial spaces where the bulk of the 
available water is held. Consequently a consideration 
of the movement of capillary moisture is necessary, not 
only as to its mechanics, but also as to the factors influ- 
encing its rate and height of movement. These factors 
are four in number: (1) thickness of water film; (2) sur- 
face tension ; (3) texture ; and (4) structure. 

152. Effect of thickness of water film on capillary 
movement. — It has been repeatedly noticed, in the 
study of the capillary adjustment between two soils, that 
the lower the percentage of water, the slower is the rate 



224 soils: properties and management 




of movement. This indicates that the thickness of the 
film covering the particles and connecting the interstices 
containing the bulk of the capillary water is, within 
certain limits, a dominant factor in rate of movement at 
least. Let it be supposed that a withdrawal of water 
occurs at A (see Fig. 37), the interstitial space between 
two particles, the water surface being represented by the 
dotted line aa. There is an immediate increase in the 

curvature of this surface, and 
water tends to flow through 
the capillary film spaces at c 
and c', toward this area of 
greater tension. If water con- 
tinues to be withdrawn at A, 
this adjustment continues 
with considerable ease until 
the film channel at c and c' 
becomes so thin as to cause 
its surface (bb') to approach the edge of the hygroscopic 
film surrounding the particle. The viscosity of the 
water gradually becomes a factor at this point, imped- 
ing the capillary adjustment toward A. This point of 
sluggish capillary movement has been designated by 
Widtsoe ^ as the point of lento-capillarity. 

The amount of capillary water delivered at any one 
point, therefore, will obviously be influenced by the 
thickness of the film and may consequently be taken 
as a measure of rate of rise. A short soil column 
should deliver more water from a constant source 
than a longer one, due to the thicker films at the sur- 

' Widtsoe, J. A., and McLaughlin, W. W. The Movement 
of Water in Irrigated Soils. Utah Agr. Exp. Sta., Bui. 115, 
pp. 223-231. 1912. 



Fig. 37. — Diagram for the ox- 
planation of the effect of 
thickness of water film about 
soil particles upon ease of 
capillary movement. 



THE FORMS OF SOIL WATER 225 

face of the former column. King ^ shows this by the 
following data : — 

Evaporation from the Surface of Sand Columns of Dif- 
ferent Lengths, their Base being in Contact with 
Free Water 



Length op Column in Inches 


Evaporation at Surface 
IN Inches a Day 


6 


.114 


12 


.111 


18 


.080 


24 


.034 


30 


.019 



Briggs and Lapham " found, in comparing the evapo- 
ration from tubes of different lengths (85 and 165 centi- 
meters, respectively) of Sea Island soil, that the shorter 
column showed over five times as much evaporation in a 
period of forty-two days. This diminished flow with the 
thinner films is a vital point in plant production, since 
wilting must occur as soon as capillary movement becomes 
too sluggish to supply moisture fast enough for normal 
development. 

The thickness of film is important also in a considera- 
tion of the height of rise in dry and moist soil respectively. 
It is evident that the rate would be much more rapid in 
the latter, but what as to total rise ? Stewart,^ in study- 

'■ King, F. IT. Principles and Conditions of the Movements 
of Ground Water. U. S. Geol. Sur., 19th Ann. Rept., Part II, 
p. 92. 1897-1898. 

^ Briggs, L. J., and Lapham, M. H. Capillary Studies. 
U. S. D. A., Bur. Soils, Bui. 19, pp. 24-25. 1902. 

' Reported by Briggs, L. J., and Lapham, M. H. Capillary 
Studies. U. S. D. A., Bur. Soils, Bui. 19, p. 26. 1902. 



226 SOILS: PROPERTIES AND MANAGEMENT 

ing the capillary limits as to the height of rise in dry and 
moist Michigan soils, found this limit much greater where 
the soil was damp. This vertical rise from a water table 
was almost three times greater, on the average, in the soil 
in which the films were originally thicker. Briggs and 
Lapham ^ found this ratio in Sea Island soil to be as high 
as four and one-half ; while Wollny ^ has shown sand with 
9.5 per cent of moisture to raise moisture from a water 
table one-half higher in six days than did the same sand 
dry. It is evident, therefore, that a soil with a thick 
capillary film will carry moisture faster than one with a 
thinner film, and also will raise the moisture higher when 
the final film adjustment has taken place. 

In an air-dry soil it is obvious that before capillarity 
may take place a thicker film than has already existed 
must be established. This is often difficult because of the 
presence of oily materials deposited on the surface of the 
particles during the process of drying out. Such a condi- 
tion probably accounts, at least partially, for the differ- 
ence in total rise of capillary water in a dry and in a moist 
soil, since, theoretically, if time enough were given for 
adjustment, the total height should be the same in both 
columns. This resistance of dry soil to the resumption 
of a capillary film is made use of in soil mulches, where a 
dry surface layer of the soil checks e^'apo^ation by imped- 
ing capillary rise. It is also obvious that in a study of the 
rate and height of capillary movement and the factors 
affecting it, moist columns should be used, as this is a 



^Briggs, L. J., and Lapham, M. H. Capillary Studies. 
U. S. D. A., Bur. Soils, Bui. 19, p. 20. 1902. 

' Wollny, E. Untersuehungen iiber die Kapillare Lcitung 
des Wassers im Boden. Forsch. a. d. Gebiete d. Agri.-Physik, 
Band 7, Seite 2G9-308. 1884. 



THE FORMS OF SOIL WATER 227 

near approach to the conditions of a field soil. Since this 
is rather a difficult study to carry out, most of the rate 
and height data on capillary movement have been largely 
obtained with dry columns in contact with free water at 
the bottom. Such data are comparative, but are far 
from quantitative as regards the performance of any soil 
under normal conditions. 

153. Surface tension and capillary movement. — As 
has already been shown, the thickness of a maximum 
capillary film is largely determined by surface tension; 
and as surface tension with any given curvature exerts a 
definite pressure, it is evident that this pressure may be- 
come greater or smaller with variations in the surface 
tension. One of the most potent factors having to do 
with this variation is temperature. If the temperature 
of a soil column in capillary equilibrium and containing 
its maximum capillary moisture should be raised, some 
of the water would be lost as free water, since the pulling 
power of the films would be decreased. In the same 
way, the capillary capacity would be increased by a lower- 
ing of the temperature, which of course would mean a 
higher capillary rise in either a dry or a wet soil. The 
rate of movement,^ however, would be facilitated in the 
first case, since the viscosity of the water would be much 
reduced, allowing the movement in the film channels to 
take place with less friction. 

King - has verified these conclusions in his experiments 



1 WoUny, E. Untersuehungen iiber die Kapillare Leitung 
des Wassers im Boden. Forsch. a. d. Gebiete d. Agri.-Physik, 
Band 8, Seite 206-220. 1885. 

^ King, F. H. Fluctuations of the Level and Rate of Flow 
of Ground Water. U. S. D. A., Weather Bur., Bui. 5, pp. 59- 
61. 1892. 



228 SOILS: PROPERTIES AND MANAGEMENT 

with the fluctuations of the ground water of a soil held 
in a large cylindrical tank. Pie found that with a lower- 
ing of temperature the ground water was lowered, due 
to the increased capillary capacity of the soil generated 
by a higher surface tension. A consequent upward move- 
ment of water took place. When the temperature was 
raised, however, there was a reverse movement, due to a 
change of capillary water to free water brought about by 
a lowered surface tension. 

The surface tension may also be varied by materials in 
solutions, most salts tending to cause increased tension. 
The addition of soluble fertilizer salts to a soil would 
therefore be expected to exert some influence. It must 
be remembered in this connection that all soils contain a 
certain amount of oily substances, produced during the 
processes of organic decay. It is probable that the lower- 
ing effect of such material would largely overbalance 
any marked influence from fertilizer salts. jNIoreover, 
as such salts are strongly adsorbed by the soil particles, 
their efi'ect on the concentration of the surface film would 
probably be light even if undisturbed by the soil resins. 
Wollny ^ has shown that adsorbed salts produce little 
effect on capillarity, while non-adsorbed salts cause a 
depression increasing with concentration. 

Briggs and Lapham ^ found that with Sea Island soil 
dissolved salts in dilute solution had no appreciable effect 
except in the case of sodium carbonate. The increased 
rise in this case they ascribe to the saponification of the 

1 Wollny, E. Untersuehungen liber die Kapillare Leitiing 
des Wassers. Forscb. a. d. Gebiete d. Agri.-Phvsik, Band 7, 
Seite 269-308. 1884. 

^ Briggs, J. B., and Lapham, M. H. Capillary Studies. 
U. S. D. A., Bur. Soils, Bui. 19, pp. 5-18. 1902. 



THE FORMS OF SOIL WATER 229 

oils on the particles, and a consequent exposure of clean 
surfaces for capillary movement. These authors found 
also that concentrated solutions reduced the rate of 
capillary movement. Davis/ in working with a silt loam, 
obtained variable results, some salts depressing and some 
accelerating capillary rise. Potassium acid phosphate 
caused the maximum retardation, while ammonium ni- 
trate most markedly increased the rate. Since only one 
soil was used and the greatest observed capillary rise was 
less than twelve inches, additional data must be presented 
before it is clear that the concentration of salts may be- 
come a very important factor in humid soils. In alkali 
soils, in which the concentration of the salts is very great, 
there is no doubt that considerable retardation may occur. 

154. Efifect of texture on capillary movement. — In 
soils of fine texture, not only is the amount of film surface 
exposed greater than in coarse soils, but the curvature of 
the films is also greater, due to the shorter radii. The 
effective pressure exerted by the films is consequently 
much higher in fine-grained soil. The greater exposure 
of surface and the increased pressure both serve to raise 
the friction coefficient and retard the rate of flow. The 
finer the texture of the soil, other factors being equal, the 
slower is the movement of capillary water. Water should 
therefore rise less rapidly from a water table through a 
column of clay than through a sand or a sandy loam. 

The height to which water may be drawn by the effec- 
tive capillary power of a soil, equilibrium being estab- 
lished, depends on the number of interstitial angles. The 
greater the number of angles, the greater is the total 

1 Davis, R. O. E. The Effect of Soluble Salts on the Physi- 
cal Properties of Soils. U. S. D. A., Bur. Soils, Bui. 82, pp. 
23-31. 1911. 



280 SOILS: PROPERTIES AND MANAGEMENT 

supporting power of the films. As a silt soil contains a 
larger number of such angles, its capillary pull is greater 
than that of a sand, and consequently the ultimate move- 
ment would be of greater scope. The finer the texture, 
then, the slower is the rate of capillary movement but the 
greater is the distance.^ 

The relation of texture to rate and height of capillary 
movement in dry soil is shown by the following un- 
published data, obtained in the laboratory of the Depart- 
ment of Soil Technology, Cornell University : — 

Effect of Texture on Rate and Height of Capillary 
Rise from a Water Table through Dry Soil 



Soil 


1 Hour 


1 Day 


2 Days 


3 Days 


4 Days 


5 Days 




Inches 


Inches 


Inches 


Inches 


Inches 


Inches 


Sand . . . 


3.5 


5.0 


5.9 


6.8 


6.8 


6.9 


Clay . . . 


.5 


5.7 


8.9 


10.9 


12.2 


13.3 


Silt .... 


2,5 


14.5 


20.6 


24.2 


26.2 


27.4 



It is seen that the movement in sand is rapid, one-half 
of the total rise being attained in one hour. The maxi- 
mum height is reached in about three days. The silt in 
this case seems to be of just about the right textural con- 
dition for a fairly rapid rise, yet it exerts enough capil- 
lary pull to attain a good distance above the water table. 
The friction in the clay is greater, however, and this 
results in a slower rate. Whether the clay would ever be 
able to exhibit a rise comparable with its tremendous pull- 



1 WoUny, E. Untersuehungen iiber die Kapillare Leitung 
des Wassers ira Boden. Forsch. a. d. Gebiete d. Agri.-Physik, 
Band 7, Seite 2G9-308. 1884. Also, Forsch. a. d. Gebiete d. 
Agri.-Physik, Baud 8, Seite 206-220. 1885. 



THE FORMS OF SOIL WATER 231 

ing capacity is doubtful, because of the resistance offered 
by the dry soil. 

155. Texture and the capillary pull of soils. — An ingen- 
ious method for measuring quantitatively the capillary 
pull exerted by a moist soil has been devised by Lynde 
and Diipre.^ The apparatus consists of a glass funnel 
joined to a thick-walled capillary tube by means of a piece 
of rubber tubing, a water seal being used at this point. 
The lower end dips into mercury. The soil to be studied 
is placed in the funnel, and after being saturated is con- 
nected by means of a wick of cheesecloth or filter paper 
to the water column previously established in the capil- 
lary tube. If no break occurs between the soil and the 
capillary water column, the apparatus is ready for use. 

The excess water having drained away, there is a 
thinning of the films on the soil surface due to evapora- 
tion. Equilibrium adjustments now take place, which 
result in the drawing upward of the water column. The 
mercury follows, and the strength of the pull may be meas- 
ured by the height of the mercury column. The old 
method of measuring capillary power by the water move- 
ment through a dry soil is vitiated by two conditions 
— the length of time necessary, and the fact that the 
maximum lift cannot be obtained due to excessive fric- 
tion. This new method .uses a wet soil, requires only 
a short time, and gives a more nearly accurate idea of the 
power of the capillary pull. It does not, however, yield 
data regarding rate of movement, — a factor of vital 
importance to plant growth, as will be shown later. 

Lynde and Dupre, in their results, confirm the state- 

1 Lynde, C. J., and Dupre, H. A. On a New Method of 
Measuring the Capillary Lift in Soils. Jour. Amer. Soe. Agron., 
Vol. 5, No. 2, pp. 107-il(i. 1913. 



232 SOILS: PROPERTIES AND MANAGEMENT 

merits already made regarding the relation of texture 
to capillary power : — 

The Capillary Lift of Soil Separates as Determined by 
Lynde and Dupre 



Soil 


Diameter op Grain, 
IN Millimeters 


LiPT OP Water 
Column, in Feet 


Medium sand .... 

Fine sand 

Very fine sand .... 

Silt 

Clay 


.5 -.25 
.25 -.10 
.10 -.05 
.05 -.005 
.005- 


.98 
1.78 

4.05 

9.99 

26.80 



The capillary pull may also be established, at least 
comparatively, by the height of the wetted soil and the 
amounts of water at various points in a soil column that 
has reached a capillary equilibrium when its base is in 
contact with a constant supply of water. The curves 
from Buckingham ^ (Fig. 34, p. 216) determined after the 
soil had stood for sixty-eight days, illustrate this. 

156. Effect of structure on capillary movement. — 
Structure has already been shown to affect capillary 
capacity by its influence on the angle interstices. P]vi- 
dently, therefore, it may alter both the rate and the height 
of capillary rise. The loosening of a clay soil or the 
compacting of a sandy soil will lessen the efl'ective film 
friction, while at the same time it will strengthen the 
capillary pull resulting in a faster and a higher capillary 
flow of water. The exact structural condition of any soil 
in which this result is realized to its highest efficiency it 
is impossible to judge exactly. In general, however, this 

1 Buckingham, E. Studies on the Movement of Soil Mois- 
ture. U. S. D. A., Bur. Soils, Bui. 38, p. 32. 1907. 



TUE FORMS OF SOIL WATER 233 

point is approached when the soil is in the best physical 
condition for crop growth. Tillage operations in general, 
tile drainage, and the addition of lime and organic matter, 
operate toward this result by their granulating tend- 
encies ; while rolling, by compacting a too loose surface, 
may accomplish the same effect but by an opposite process. 
At certain seasons of the year capillarity must be 
impeded near the surface, as it continually pumps val- 
uable water upward to be lost by evaporation. This 
movement ma^^ be checked by producing on the soil sur- 
face, by appropriate tillage, a layer of dry, loose soil. 
This layer, called a soil mulch, affords much resistance 
to wetting because of its dryness, while at the same time 
it affords but little surface and few angle interstices for 
effective capillary pull. Thus it is that a farmer, in order 
to meet his immediate or future needs, may alter and 
control capillary movement by careful attention to phys- 
ical conditions, especially those at the surface where 
evaporation is always active. 

157. Gravitational water. — As soon as the capillary 
capacity of a soil column is satisfied, further addition of 
moisture will cause the appearance of free water in the air 
spaces. By the attraction of gravity, this water moves 
downward through the earth at a rate varying with soil 
and climatic conditions. In general the flow is governed by 
four factors — pressure, temperature, texture, and structure. 
An understanding of the operation of these forces is im- 
portant, since the rapid elimination of free water from the 
soil is necessary for optimum plant growth. The actual 
procedure, however, is considered under the head of " Land 
Drainage," a distinct phase of soil management in itself. 

158. Pressure and the movement of gravity water. — 
It is very evident that any pressure exerted on a water 



234 SOILS: PROPERTIES AND MANAGEMENT 

column will accelerate the rate of flow. Under normal 
conditions pressure may arise from two sources, baro- 
metric ])ressure and the weight of the water column. 
Changes in barometric pressure are communicated to 
gravitational water through a movement of the soil air. 
As the mercury column rises, more air is forced into the 
soil and the pressure on the soil water increases. Such 
a change has been observed by King ^ to produce as high as 
a 15 per cent increase in the flow of drains. King observed 
also that the level of wells fluctuated from time to time for 
the same cause. The ex]3ansion of the air of the soil due to 
daily heatings was also ol)served to produce diurnal oscil- 
lations in the level and the rate of flow of ground water. 
Perhaps of greater import in the rate of percolation of 
water is the pressure produced by the weight of the free- 
water column. Working along this line, Welitschkowsky ^ 
has shown rather conclusively that with an ideal length of 
column the flow varies directly with the pressure. His 
ideal column with the sand w^ith which he ex])erimented 
was 75 centimeters in length. With a longer column the 
flow did not increase as fast as the pressure ; while with 
a shorter column, doubling the pressure more than doubled 
the flow. These results have been verified by Wollny ^ 
and ably reviewed by King.^ 



1 King, F. H. The Soil, p. 180. New York. 1906. 

2 Welitschkowsky, D. von. Experimentelle Untersuchun- 
gen iiber die Permeabilitilt des Bodens fur Wasser. Archiv f. 
Hygiene, Band II, Seite 499-512. 1884. 

^ Wollny, E. Untersuehungen iiber die Permeabilitiit des 
Bodens fur Wasser. Forsch. a. d. Gebietc d. Agri.-Physik, 
Band 14, Seite 1-28. 1891. 

^ King, F. H. Principles and Conditions of the Movements 
of Ground Water. U. S. Geol. Survey, 19th Ann. Rept., Part 
11, pp. 07-200. 1897-98. 



THE FORMS OF SOIL WATER 235 

159. Effect of temperatiire on the flow of gravity water. 
— A rise in tem]jerature of the soil not only varies the 
amount of capillary water and thus increases the possible 
free water present, but at the same time it increases the 
fluidity and thus facilitates percolation. The expansion 
of the soil air also tends to increase such movement. This 
can be noticed in the operation of a tile drain in early 
spring as compared with summer conditions. Calculated 
effects of temperature change have been verified by con- 
trolled experimental results. 

160. Effect of texture and structure on the flow of 
gravity water. — Of much more practical importance 
than temperature, in the flow of gravitational water, 
are the size and the arrangement of the soil particles. 
In working with sands of varying grades, Welitschkowsky,^ 
Wollny,^ and others have shown that the flow of water 
varies with the size of particle, or texture. King ^ has 
demonstrated that in general with such materials the 
rate of flow is directly proportional to the square of the 
diameter of the particle. By the use of the effective 
mean diameter ■* of a sand sample, he was able to calculate 
a theoretical flow which compared very closely to observed 
percolations. In sandy soils this law holds in a very 
general way, but in clays it fails entireh'. For instance, 

^ Welitsehkowsky, D. von. Experimentelle Untersuchungen 
uber die Permeabilitiit des Bodens fiir Wasser. Archiv f. 
Hygiene, Band II, Seite 499-512. 1884. 

^ WoUny, E. Untersuchungen iiber den Einfluss der 
Struktur des Bodens auf dessen Feuchtigkeits- und Tempera- 
turverhaltnisse. Forseh. a. d. Gebiete d. Agri.-Physik, Band 
5, Seite 167. 1882. 

^ King, F. H. Principles and Conditions of the Movements 
of Ground Water. U. S. Geol. Survey, 19th Ann. Kept., Part 
II, pp. 222-224. 1897-98. 

■* This text, paragraph 87. 



236 SOILS: PROPERTIES AND MANAGEMENT 

if such a law was in force a sand having a diameter of 
.5 millimeter would exhibit a flow 10,000 times greater 
than that through a clay loam with a diameter, say, of 
.005 millimeter; whereas the actual ratio, as observed 
experimentally by King, was less than 200. 

Evidently, therefore, while it can be stated as a general 
thesis that the flow varies with the texture, no governing 
law can be deduced for soils since structure exerts such a 
modifying influence. The percolation in a heavy soil 
takes place largely through lines of seepage, which are 
really large channels developed by various agencies. 
If in the drainage of average soil, the farmer depended 
on the movement of water through the individual pore 
spaces, the soil would never be in a condition for crop 
growth. These lines of seepage are developed by the 
ordinary forces that function in the production of soil 
granulation, as freezing and thawing, wetting and drying, 
lime, humus, plant roots, and tillage operations. 

A clear understanding of the factors governing the 
flow of gravitational water is of especial importance in 
tile drainage operations, particularly regarding the depth 
of and interval between tile drains. Since percolation 
is so slow in a heavy soil, it is evident tliat the tile must 
be near the surface in order to secure efficient drainage. 
In a sand the depth may be increased, because of the 
slight resistance offered to water movement. The depths 
for laying tile in a heavy soil range from one and a half 
to two and a half feet, while in a sand the tile may often 
be placed as deep as four feet below the surface. It is 
evident also that the less deep a tile drain is laid, the 
less distance on either side it will be effective in removing 
the water ; consequently on a clay soil the laterals must 
be relatively close, as compared to the interval generally 



THE FORMS OF SOIL WATER 237 

recommended for a sandy soil. A rational understanding 
of the movements of gravitation water is clearly necessary 
in the installation of tile drains, not only that the system 
may be fully effective, but also that a minimum effective 
cost may be realized. 

161. Determination of the quantity of free water that 
a soil will hold. — While there is no particular advantage 
in finding the quantity of gravitational water that a soil 
will hold, since a normal soil should never remain saturated 
for any length of time, it is nevertheless of interest to 
know by what methods such data may be obtained. One 
method is to saturate a column of known weight, and 
then, by exposing it to percolation, measure the amount 
of water that is lost. The gravitational water can then 
be expressed in terms of dry soil. The disadvantage in 
this method lies in the fact that it is extremely difficult 
to free a soil entirely of air, so that a determination made 
in this way would yield low results. Again, a very long 
time must elapse before a soil will give up all its gravita- 
tional water. King ^ found that with even a sand the 
draining-away of the free water continued over a space 
of two and one half years. It must also be noted here 
that because of the lessening of the capillary water as a 
column of soil is ascended, the space for possible free 
water increases, thus accounting for the ready entrance 
of rain into a -soil which on the average may contain a 
relatively high water content. 

162. The calculation of the free water of a soil. — A 
more nearly accurate idea of the possible free-water 
capacity of soil may be obtained by calculation. If the 
absolute and the apparent specific gravity of a soil, and 

1 King, F. H. Phj'sics of Agriculture, pp. 134-135. Pub- 
lished by the author, Madison, Wisconsin. 1910. 



238 SOILS: PROPEHriES AND MANAGEMENT 

its percentage of moisture when capillarily satisfied, are 
knoAvn, the following formula may be usefl : — 



Percentage of air space when 
capillarily saturated 



['percentage of pore space 
— (percentage of II2O 
X ap. sp. gr.) 



Percentage of free water pos- ] _ f pe rcentage of air space 
sible J [ ap. sp. gr. 

163. Value of studying flow and composition of gravita- 
tional water. — While the determination of the possible 
free water that a soil will hold is of little real value, a 
knowledge of its movement and its composition is of 
vital importance. It has already been shown how the 
rate of movement of such water is a factor in efficient 
drainage. The amount likely to be thus lost is of interest 
in plant production from two standpoints : first, the 
role that water plays as a food and a regulator ; and 
secondly, the losses of nutritive elements that always 
occur with drainage. It is quite e^•ident that these 
questions should be studied only on soil in a normal field 
position. Consequently two methods of procedure are 
open — the use of an efficient system of tile drains, and 
the construction of lysimeters. 

164. The study of gravity water by means of tile drains. 
— In the first method an area should be chosen where 
the tile drain receives only the water from the area in 
question and where the drainage is efficient. A study 
of the amounts of flow throughout a term of years will 
yield much valuable data concerning the factors already 
discussed. An analysis of the drainage water will throw 
light on the ordinary losses of ]:)lant-food from a normal 
soil under a known cropping system. The advantage 



THE FORMS OF SOTL WATER 



239 



of such a method of attack Hes not only in the fact that 
a large area of undisturbed soil is considered, but also 
in the opportunity to study practical field treatments 
in relation to the movement and composition of drainage 
water. 

165. The lysimeter method of studying gravitational 
water. — The lysimeter method, however, has been the 
usual mode of attacking these problems. In this method 
a small block of soil is used, being entirely isolated by 
appropriate means from the soil surrounding it. Effective 
and thorough drainage is provided. The advantages of 
this method are that the variations found in a large field 
are avoided, the work of carrying on the study is not so 
great as in a large field, and the experiment is more easily 
controlled. One of the best-known sets of lysimeters 
was that established at the Rothamsted Experiment 



^re7c/e 



" 






— ,- 








..■_•;.. ■_..;.■...:... •.•■.•• .■• ■.••■".• •■ 


zc 


^ 






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1 1 




/? 




^■^M:^;:^:^^\\^'ev-^T^ 


■zn 


/7 












•'.v''^:'---'v.';-''-- ■■;■■':' ■■■:■■.'■•■•■'■' 


-1- 








\^°'' ^^-^^ 










1 
I 
















v.';/ ■ 




"\/^ 


— L_ 




*'. *•••..■■■ 




— i — . 




'.*.•■ 










p^^^ 


hj= 


























1 I 










1 




^••. ., ■ . ■ 






L^:. 








1 .'.'.'■'.' . 


— I— 
I - 






li.'. '■'. 1. ''..'■■.■'. J...'. ^ .'..' 





Fig. 38. — Cross section of a lysimeter at the Rothamsted Experiment 
Station, England. (/('), soil column under study; (p), outlet for 
collected drainage water. 



240 SOILS: PROPERTIES AND MANAGEMENT 

Station ^ in England, (See Fig. 38.) Here blocks of 
soil one one-thousandth of an acre in surface area were 
isolated by means of trenches and tunnels, and, supported 
in the meantime by perforated iron plates, were separated 
from the surrounding soil by masonry. The blocks of soil 
were twenty, forty, and sixty inches in depth, respectively. 
Facilities for catching the drainage were provided under 
each lysimeter. The ad\antage of such a method of 
construction lies in the fact that the structural condition 
of the soil is undisturbed and consequently the data are 
immediately trustworthy. 




Ti/nne/ 






\^ 6 5e»er Te 



y 1 



o 



Fig. 39. — Cross section of a soil tank at Cornell University, New 
York, (rt), soil under investigation ; (p), outlet of drainage pipe. 



' Lawes, J. B., Gilbert, J. H., and Warington, R. On the 
Amount and Composition of the Rain and Drainage Waters 
Collected at Rothamsted. Jour. Roy. Agr. See., Ser. II, Vol. 
17, pp. 2G9-271. 1881. 



THE FORMS OF SOIL WATER 241 

At Cornell University ^ a system of cement tanks sunk 
in the ground has been constructed. Each tank is about 
four and a half feet square and four feet deep. A sloping 
bottom is provided, with a drainage channel opening into 
a tunnel beneath and at one side. As the tanks are ar- 
ranged in two parallel rows, one tunnel suffices for both. 
(See Fig. 39.) The sides of the tanks are treated with 
asphaltum in order to prevent solution. The soil must 
of course be placed in the tanks, this causing a disturb- 
ance of its structural condition. As a consequence data 
as to rate of flow and composition of the drainage water 
are rather unreliable for the first few years. Such an 
experiment must necessarily be one of long duration. 

166. Thermal movement of water. — Little has been 
said as yet regarding this third mode of water movement, 
the vapor flow, which is not peculiar to one form of soil 
water but affects all alike. It is at once apparent that 
the movement of water vapor can be of little importance 
within the soil itself, since it depends so largely on the 
diffusion and convection of the soil air. While the soil 
air is no doubt practically always saturated with water 
vapor, the loss of moisture by this means is slight. Buck- 
ingham - has shown that, while sand allows such a move- 
ment to the greatest degree, the loss occurring in a soil 
with any appreciable depth of layer is almost negligible. 

The question of the thermal movement of water at the 
soil surface, however, is vital in farming operations. At 
this point the water films are exposed to sun and wind, 
and drying goes on rapidly, the free, capillary, and a 

1 Lyon, T. L. Tanks for Soil Investigation at Cornell Uni- 
versity. Science, N. Ser., Vol. 29, No. 74G, pp. 621-623. 1909. 

- Buckingham, E. Studies on the Movement of Soil 
Moisture. U. S. D. A., Bur. Soils., Bui. 38, pp. 9-18. 1907. 

R 



242 SOILS: PROPERTIES AND MANAGEMENT 

part of the hygroscopic water vaporizing in the order 
named. If the loss of the surface moisture were the 
only consideration, the problem would not be serious ; 
but the capillarity of the soil must be considered also. 
As the films at the surface become thin a capillary move- 
ment begins, and if the evaporation is not too rapid a 
very great loss of water may occur in a short time. 

The evaporation from a bare soil in the Rothamsted 
lysimeters ^ averaged about seventeen inches a year, 
with a rainfall ranging from twenty-two to forty-two 
inches. This means that from one-third to one-half of 
the effective rainfall was entirely lost as thermal water. 
The necessity of checking such a loss becomes apparent, 
especially in regions where rainfall is slight or drought 
periods are likely to occur. As no country is free from 
one or the other of such contingencies, the great promi- 
nence that methods of moisture conservation hold in 
systems of soil management is understandable. While 
means of checking losses by leaching and run-off are 
advocated, effective retardation of surface evaporation 
is always particularly emphasized. 

1 Warington, R. Physical Properties of the Soil, p. 109. 
Clarendon Press, Oxford. 1900. 



CHAPTER XII 

THE WATER OF THE SOIL IN ITS RELA- 
TION TO PLANTS 

Water, as has already been shown, is one of the external 
factors in plant growth in that it is necessary in the 
processes of weathering, which results in the simplifica- 
tion of compounds for plant utilization. It also func- 
tions as an internal factor in plant development, inasmuch 
as it maintains the turgidity of the plant cells, acts as a 
carrier of food materials, functions as a regulator, and 
can actually be utilized as a source of hydrogen and 
oxygen. These direct or indirect functions of water in 
relation to plant growth may be considered under three 
heads, as follows : — 

167. Functions of water to the plant. — 

1. JVater acts as a solvent and a carrier of plant-food 

materials. It is therefore a medium of transfer 
for the mineral and gaseous elements from the 
soil to their proper places within the plant. 

2. As a food water either becomes a part of the cell 

without change, or is broken down and its ele- 
ments are utilized in new compounds. 

3. Water in maintaining turgidity, in equalizing the 

temperature by evaporation from the leaves, and 
in facilitating quick shifts of food from one part 
of the plant to another, acts as a regulator during 
assimilation and while synthetic and metabolic 
processes are going on. 
243 



244 SOILS: PROPERTIES AND MANAGEMENT 

Soil moisture, therefore, in proper amounts, becomes 
one of the controUing factors in crop growth and must 
be looked to before the maximimi utilization of the 
primary elements can be expected. The amount of 
water held within the plant is not large, however, in 
comparison with the amount lost by transpiration, al- 
though green plants contain from 60 to 90 per cent of 
moisture. The main cause of the high transpiration of 
most crops is traceable to the dilute condition of the 
soil solution, although certain regulatory functions may 
also come into play. 

Since relatively few parts to a million of nitrogen, 
phosphorus, and potash are carried by the soil solution, 
large quantities of water must be taken up in order that 
sufficient quantities of food may be supplied to the plant. 
This excess water is largely lost or disposed of by trans- 
piration, at the same time performing its regulatory 
functions. 

168. The water requirement of plants. — As might be 
expected, the pounds of water transpired for every pound 
of dry matter produced in the crop is very large. This 
figure, called the transpiration ratio, or water require- 
ment, ranges from 200 to 500 for crops in humid regions, 
and almost twice as much for crops in arid climates. 
An accurate determination of the transpiration ratio of 
a crop is somewhat difficult, due to the methods of pro- 
cedure necessary and also to the difficulty of controlling 
the numerous factors that may vary the transpiration. 
For really reliable figures the plants must be grown in 
cans or pots, in order that the water lost may be deter- 
mined accurately by weighing. If there is no percolation, 
the water ordinarily lost from a cropped soil includes 
both that evaporated from the soil surface and that 



WATER OF SOIL IX ITS RELATION TO PLANTS 245 

transpired from the leaves. The former loss may be 
eliminated from calculations in two ways : (1) by covering 
the soil in some way so that evaporation is absolutely 
checked and the only loss is by transpiration ; or (2) by 
determining the evaporation from a bare pot and, by 
subtracting this from the total water loss from a cropped 
soil, finding the loss due to transpiration alone. 

An objection to the former method is that any covering 
which interferes with evaporation interferes with proper 
soil aeration also and may render soil conditions abnormal. 
In the second method, however, an even more serious 
error enters, since the evaporation from a bare soil is 
not the same as that from a soil covered by vegetation 
because of the shading effects. Also, due to the action 
of the roots, less water is likely to be allowed to move 
to the surface by capillary attraction in the cropped soil. 
Therefore, any data that may be quoted can be only 
general in its application, not only because of the errors 
of determination but also because of the great number of 
factors that under normal conditions may vary the 
transpiration ratio. The data on the following page, 
drawn from various investigators working by the gen- 
eral methods ^ already outlined, give some idea of the 
water transpired by different crops, due allowance being 
made for various disturbing factors. Below the data 
regarding transpiration will be found the citations to 
the work of the various authors as well as a few 
notes regarding their experimental procedure. 

' A brief discussion of the various methods is found as follows : 
Montgomery, E. G. Methods of Determining the Water 
Requirements of Crops. Proc. Amer. Soc. Agron., Vol. 3, 
pp. 261-283. 1911. Also Briggs, L. J., and Shantz, H. L., 
The Water Requirement of Plants. U. S. D. A., Bur. Plant 
Ind., Bui. 285. 1913. 



246 SOILS: PROPERTIES AND MANAGEMENT 



Water Requirements of Plants by Different 
Investigators 



Cbop 


1 « J 


Wollny' 

Munich 

Germany 1876 


Hellriegel' 

Dahme 

Germany 

1883 


KlNG< 

Madison 

Wisconsin 

1805 


Leather ^ 
Pusa 
India 
1911 


9 2„ 

Z" Oi-H 

= < z^ 
2 = 0- 


Barley 


258 


774 


310 


464 


468 


534 


Beans 


209 


— 


282 


— 


— 


736 - 


Buckwheat . . . 


— 


646 


363 


— 


— 


578 


Clover 


269 


— 


310 


576 


— 


797- 


Maize 


— 


233 


— 


271 


337 


368 ' 


Millet 


— 


447 


— 


— 


— 


310 ~ 


Oats 


— 


665 


376 


503 


469 


597 


Peas 


259 


416 


273 


477 


563 


788 - 


Potatoes .... 


— 


— - 


— 


385 


— 


636 


Rape 


— 


912 


— 


— 


— 


441 


Rye 


— 


— 


353 


— • 


— 


685 


Wheat 


247 


— 


338 


— 


544 


513 



' Lawes, J. B. Experimental Investigation into the Amount 
of Water Given off by Plants during their Growth. Jour. 
Hort. Soc. London, Vol. 5, pp. 38-63. 1850. 

Pots holding 42 pounds of field soil were used. Evaporation 
from soil was reduced to a very low degree by perforated glass 
covers cemented on the pots. The figures quoted are from 
unfertilized soil. 

- Wollny, E. Der Einfluss der Pflanzendecke und Beschat- 
lung auf die Physikalischen Eigensehaften und die Frucht- 
barkeit des Bodens, Seite 125. Berlin, 1877. 

Wollny grew plants in humous sand in amounts ranging from 
5 to 12 kilograms. Evaporation was reduced to a very low 
degree by perforated covers. Actual evaporation from un- 
cropped cans was observed, however. 

' Hellriegel, H. Beitnige zur den Naturwissenschaftliehen 
Grundlagen des Ackerbaus, Seite 663. Braunschweig, 1883. 

Hellriegel grew jjlants in 4 kilograms of clean quartz sand 
and supplied them with nutrient solutions. The loss by evap- 
oration from uncropped pots was used in determining losses 



WATER OF SOIL IN ITS RELATION TO PLANTS 247 

169. Factors affecting transpiration. — These figures 
serve to indicate not only the variation between crops, 
but also the great effect of climate and soil on transpira- 
tion.^ The factors may be listed under three heads, as 
follows : — 



• A complete review of the literature concerning the climatic 
and soil factors in their qffect on transpiration may be found 
as follows : Briggs, L. J., and Shantz, H. L. The Water 
Requirement of Plants. U. S. D. A., Bur. Plant Ind., Bui. 
285. 1913. 



by transpiration. In later experiments covers were used in 
order to cut down evaporation. 

'' King, F. H. Physics of Agriculture, p. 139. Published 
by author, Madison, Wisconsin, 1910. Also, The Number of 
Inches of Water Required for a Ton of Dry Matter in Wis- 
consin. Wisconsin Agr. Exp. Sta., 11th Ann. Rept., pp. 240- 
248. 1894 ; and The Importance of the Right Amount and 
Right Distribution of Water in Crop Production. Wisconsin 
Agr. Exp. Sta., 14th Ann. Rept., pp. 217-231. 1897. 

King used cans holding about 400 pounds of soil. Some were 
set down into the earth while others were not. Part of the 
work was carried on in the field ; the remainder was run in 
vegetative houses. Normal soils were used. Evaporation 
from soil was very low, water being added from beneath. The 
data quoted are the average of a large number of tests. 

'" Leather, J. W. Water Requirements of Crops in India. 
Memoirs, Dept. Agr., India, Chem. Series, Vol. I, No. 8, pp. 
133-184, 1910, and No. 10, pp. 205-281. 1911. 

Jars containing from 12 to 48 kilograms of soil were used. 
Loss by evaporation was determined on bare pots. The plants 
were grown in culture houses or in screened inclosures. 

'■ Briggs, L. J., and Shantz, H. L. Relative Water Require- 
ment of Plants. U. S. D. A., Jour. Agr. Research, Vol. Ill, 
No. 1, pp. 1-63. 1914. Also, The Water Requirements of 
Plants. U. S. D. A., Bur. Plant Ind., Bui. 284. 1913. 

Plants were grown in cans holding 250 pounds of soil. Evap- 
oration from soil was prevented by means of a paraffin covering. 
Work was conducted in screened inclosures. The data are the 
average of several years' work. 



248 SOILS: PROPERTIES AND MANAGEMENT 

1. Croj). — Differences due to different crops and to 

variations of the same crop. 

2. Climate. — Rain, humidity, sunshine, temperature, 

and wind. 

3. Soil. — Moisture and general fertihty. 

170. Effect of crop and climate on transpiration. — 
Not only do different croj)s show a variation of tran- 
spiration in the same season, but the same crop may give 
a totally different transpiration in different years. This 
is due in part to inherent differences in the crop itself. 
For example, leaf surface or root zone would totally 
alter the transpiration relationship under any given 
condition. However, a great deal of the variation ob- 
served in the ratios already quoted arises from differences 
in climatic conditions. As a general thing, the greater 
the rainfall, the higher is the humidity and the lower is 
the relative transpiration. This accounts for the high 
figures obtained by Widtsoe ^ in arid Utah. Mont- 
gomery ^ found, in studying the water requirements of 
corn under greenliouse conditions, that an increase in 
the percentage humidity from 42 to 65 lowered the tran- 
spiration ratio from 340 to 191. In general, temperature, 
sunshine, and wind vary together in their effect on tran- 
spiration. That is, the more the sunshine, the higher is 
the temperature, the lower is the humidity, and the 

1 Widtsoe, J. A. Production of Dry Matter with Differ- 
ent Quantities of Irrigation Water. Utah Agr. Exp. Sta., 
Bui. 116. 1912. Also, Irrigation Investigations. Factors In- 
fluencing Evaporation and Transpiration. Utah Agr. Exp. 
Sta., Bui. 105. 1909. 

2 Montgomery, E. G., and Kiesselbach, T. A. Studies in 
Water Requirements of Corn. Nebraska Agr. Exp. Sta., 
Bui. 128, p. 4. 1912. 



WATER OF SOIL IN ITS RELATION TO PLANTS 249 

greater is likely to be the wind velocity. All this would 
tend to raise the transpiration ratio. 

171. Effect of soil moisture on transpiration. — From 
the soil standpoint, however, the factors inherent in the 
soil itself are of more vital importance as regards tran- 
spiration, since they can be controlled to a certain extent 
under field conditions. An increase in the moisture con- 
tent of a soil usually results in an increased transpiration 
ratio. The work of Hellriegel ^ w'ith barley grown in 
quartz sand containing a nutrient solution ma}' be cited 
in this regard, together with the data obtained by Mont- 
gomery ^ at Lincoln, Nebraska, with corn grown in a 
loam soil : — 

Effect of Soil Moisture on Transpiration 



Barley — Hellriegel 


Corn — Montgomery 


Soil Moisture Per- 
centage of Total 
Capacity 


Transpiration 
Ratio 


Soil Moisture Per- 
centage of Total 
Capacity 


Transpiration 
Ratio 


80 
60 
40 
30 
20 
10 


277 
240 
216 
223 
168 
180 


100 

80 

60 

4.5 

35 


290 
262 
239 
229 
252 



These data show clearly that an excessive amount of 
water in the soil is not a favorable condition for the 



^ Hellriegel, H. Beitrage zu den Naturwissensehaftlichen 
Grundlagen des Ackerbaus, Seite 639. Braunschweig. 1883. 

- Montgomery, E. G. Methods of Determining the Water 
Requirements of Crops. Proe. Amer. Soc. Agron., Vol. 3, 
p. 276. 1911. 



250 SOILS: PROPERTIES AND MANAGEMENT 

economic use of water, as the plant, in order to supply 
itself properly with food, must transpire excessive junounts 
of water. As soil moisture may be controlled, this waste 
may to a certain extent be eliminated. 

172. The influence of fertility on transpiration. — The 
amount of uvaihible plant-food is also concerned in the 
economic utilization of water. In general the data along 
these lines show that the richer the soil, the lower is the 
transpiration ratio. Therefore a farmer, in raising the 
general fertility of his soil by drainage, lime, good tillage, 
green manures, barnyard manures, and fertilizers, provides 
at the same time for a greater amount of plant production 
for every unit of water utilized. Again, quoting from 
Hellriegel and Montgomery, the following figures are 
available : — 



Effect of the Supply of Plant-food Materials on the 
Tran.spiration Ratio of Barley grown in Quartz Sand 
WITH A Nutrient Solution ; Calcium Nitrate being in 
THE Minimum. Hellriegel ^ 



Units 2 of Ca(N03)2 
Applied 


Dry Matter Produced 
PER Pot (Grams) 


Transpiration Ratio 





1,111 


724 


4 


8,479 


399 


8 


13,936 


347 


12 


18,288 


345 


16 


23,026 


302 


20 


25,504 


292 



> IloUriegel, H. Beitriige zu don Naturwissonsohaftlichen 
Grundlage des Ackerbaus, p. 629. Braunschweig. 1883. 

- A unit of Ca(N03)2 equals 1 mg.-equivalent. A mg.- 
equivalent of Ca(N03)2 equals 82.1 mg. 



yVATER OF SOIL IN ITS RELATION TO PLANTS 251 



Relative Water Requirements of Corn on Different 
Types of Nebraska Soils, 1911. Montgomery i 



Soil 


Dry Weight op Plants 
IN Grams per Pot 


Transpiration Ratio 




Manured 


Unmanured 


Manured 


Unmanured 


Poor (15 bushels) . . 
Medium (30 bushels) . 
Fertile (50 bushels) . . 


376 
413 
472 


113 
184 
270 


350 
341 
346 


549 

479 

■ 392 



173. Effect of texture on transpiration. — The effects 
of texture have been investigated by a number of men, 
the work of Von Seelhorst^ and of Widtsoe^ being per- 
haps the most rehable. While these investigators found 
in general that crops on heavy soils exliibited a lower 
transpiration ratio, hasty conclusions must not be drawn. 
Since the fine-textured soils contain more plant-food 
materials, it is probable that this is the balancing factor 
rather than texture alone. 

174. Actual amounts of water necessary to mature a 
crop. — Although it can be seen from the transpiration 
ratio that the amount of water necessary to bring an 
average crop to maturity is very large, a concrete example 
may be cited to advantage. A fair estimate of the dry 
matter produced in raising a forty-bushel crop of wheat 
would be about two tons. Assuming the transpiration 



^ Montgomery, E. G. Water Requirements of Corn. 
Nebraska Agr. Exp. Sta., 2.5th Ann. Rept., p. xi. 1912. 

^ Seelhorst, C. von. Uber den Wasserverbrauch von 
Roggen, Gerste, Weizen, und Kartoffeln. Jour. f. Land- 
wirtschaft. Band 54, Heft 4, Seite 316-342. 1906. 

^ Widtsoe, J. A. Irrigation Investigations. Factors Influ- 
encing Evaporation and Transpiration. Utah Agr. Exp. Sta., 
Bui. 105. 1909. 



252 SOILS: PROPERTIES AND MANAGEMENT 

ratio to be 300, the amount of water actually used by 
tlie plant would amount to 600 tons to the acre, or about 
5.2 inches of rainfall. This does not include the evapora- 
tion that is continually going on from the soil surface, 
which might very easily amount to as much more. IMore- 
over, this draft on the soil water is not a uniform one, but 
increases gradually as the crop develops, until at heading 
time great quantities must be supplied in a short period. 
The necessity of moisture conservation in order to meet 
the plant requirements and preserve its normal develop- 
ment, even in humid regions, becomes obvious. 

175. Role of capillarity in the supplying of the plant 
with water. — A query arises at this point regarding the 
mode by which this immense quantity of water is supplied 
to the plant. The plant rootlets, especially their absorb- 
ing surfaces, are few in number as compared with the 
interstitial angles that contain most of the water retained 
in the soil. How, then, does the plant avail itself of 
water not in immediate contact with its rootlets? This 
question has been anticii)ated in the discussion concern- 
ing the capillary equilibrium which tends to occur in all 
soils. As soon as the rootlet begins to absorb at one 
point, the film in that interstitial angle (see Fig. 36) is 
thinned. A considerable convexity of the water surface 
occurs at that point, resulting in a great outward pull 
which causes the water to move in all directions toward 
that point. Thus, a feeding rootlet, by absorbing some 
of the soil solution with which it is in contact, creates a 
condition of instability which results in considerable 
film movement. It can therefore be said that capillarity 
is the important factor in any soil in supplying the plant 
with proper quantities of moisture. 

Many of our early investigators have overestimated 



WATER OF SOIL IN ITS RELATION TO PLANTS 253 

the distances through which this movement may be 
effective in properly supplying the plant.^ It must be 
understood, however, that the rate of water supply is 
the controlling factor in plant nutrition. It has been 
shown also that the longer the capillary column, the less 
is the amount of water delivered from a water table to 
any given point. Therefore capillarity, although it 
may act through a distance of ten feet, may be important 
for only three feet as far as plant nutrition is concerned, 
since water beyond that point is moved too slowly to be 
of any great value in time of need. No reliable data are 
available as to this particular phase, but the knowledge 
of the factors governing capillary movement clearly 
indicates that capillarity of the soil is of greatest im- 
portance in a restricted zone immediately around each 
absorbing root surface. 

176. Influence of water on the plant.^ — In general, 
as the amount of water available to a crop is increased, 
the vegetative growth also is increased, the plant be- 
coming more succulent. The percentage of moisture in 
the crop, even at harvest time, is usually high. Quality 
practically always suffers with such a stimulation of 
vegetative activity. This is especially noticeable with 
such crops as barley and peaches. Shipping qualities 
also are depressed with increased water, especially if 
the water available is excessive. With an enlargement 
of the plant cell a change probably occurs in the cell 
contents, tending toward a greater siisceptibility to 
disease. Ripening is delayed, tillering is diminished, 

1 Warington, R. Physical Properties of Soil, p. 105. Ox- 
ford. 1900. 

^ Mitscherlich, E. A. Das Wasser als Vegetationsfaktor. 
Laadw. Jahr., Band 42, Seite 701-717. 1912. 



254 SOILS: PROPERTIES AND MANAGEMENT 

and the percentage of protein content of the crop is de- 
creased. It is a curious fact, as will be shown later, that 
many of the general and morphological effects of large 
quantities of available water on plant growth are the 
same as those from the presence of too much soluble 
nitrogen. In cereals the stimulation of increased wat^r 
is shown especially in the ratio of grain to straw. Widt- 
soe's ^ results in this regard are representative of the 
data ^ available on this point : — 

Distribution of Dry Matter between Grain and Straw 
WITH Varying Amounts of Water 



Inches of Water 


Grain in Percentage op 
Total Dry Matter 


5 


44.4 


7h 


43.2 


10 


42.8 


15 


40.8 


25 


38.6 


35 


37.5 


50 


32.9 



As a general rule this depression of the ratio of grain 
to straw is not due to an actual decrease in the grain, but 
to a correspondingly greater production of dry matter in 

' Widtsoe, J. A. The Production of Dry Matter with 
Different Quantities of Irrigation Water. Utah Agr. Exp. 
Sta., Bui. 116, p. 49. 1912. 

^ Bunger, H. Uber den Einfluss Verschieden Hohen Was- 
sergehalts des Bodens in den Einzelhen Vegetationsstadien 
bei Verschiedenem NiihrstoffreichtuTn auf die Entwieklung 
des Haferpflanzen. Landw. Jahrb., Band 35, Seite 941-1051. 
1906. Also, Seelhorst, C. von, und Freekmann, W. Der 
Einfluss des Wassergehaltes des Bodens auf die Ernten und 
die Ausbilding Versehiedener Getriedevarietaten. Jour. f. 
Landw., Band 51, Seite 253-269. 1903. 



WATER OF SOIL IN ITS RELATION TO PLANTS 255 

the vegetative parts. As available water increases this 
dry matter ascends until a maximum is reached. The 
general relationships are well exemplified by data from 



1^ 

^6 









...-— ^ 










r' 


^^ 








co/2/y 




1 
































______ 






1^ fie AT 




/ 


""^ 












...-— 


^^ 






~ Por^To 


£•5 

















Ftg. 40. 



The effect of increased water supply on the production of 
dry matter by various crops. 



Widtsoe/ tabulated on the following page, although 
other equally valuable figures may be obtained from Von 
Seelhorst - and Atterberg.- The curves above (Fig. 40) 
illustrate Widtsoe's data and the general trend in the 
dry matter produced as the moisture is increased. 



1 Widtsoe, J. A. The Production of Dr.y Matter with Dif- 
ferent Quantities of Irrigation Water. Utah Agr. Exp. Sta., 
Bui. IIG, pp. l!)-2o. 1912. 

^ Seelhorst, C. von, und Krzymowski, Dr. Versueh iiber 
den Einfluss, welchen das Wasser in dem Verschiedenem Vegeta- 
tionsstadien des Hafers auf sein Wachstum auslibt. Jour. f. 
Landw., Band 53, Seite 357-370. 1905. Also, Atterberg, A. 
Die Variationen der Niihrstoffgehalte bei dem Hafer. Jour. f. 
Landw., Band 49, Seite 97-113. 1901. 



256 SOILS: PROPERTIES AND MANAGEMENT 



Crop Yield in Pounds to tub Acre as Influenced by 
Different Amounts of Water. Widtsoe 



Inches 


Dry 


Inches 


Dry 


Inches 


Dry 


Matter 


OF 


Matter 


OP 


Matter 




Wheat 


Water 


Corn 


Water 


Potato 


18.74 


4,969 


13.04 


10,757 


11.17 


2310 


21.24 


5,545 


15.. 54 


12,762 


13.67 


2730 


23.74 


. 5,684 


20.54 


13,092 


16.17 


2925 


28.74 


6,279 


25.54 


13,856 


21.17 


3405 


38.74 


6,672 


30.54 


14,606 


26.17 


4005 


48.74 


7,229 


35.54 


15,294 


36.17 


3660 


63.74 


7,999 


60.54 


12,637 


51.17 


3797 



177. Availability of the water in the soil. — From the 
discussion already presented regarding the forms of water 
in the soil, the ways in which they are held, and their 
movements, it is evident that all the moisture present 
in a soil is not available for plant growth. Three divisions 
of the soil water may be made on this basis : unavailable, 
available, and super-available. 

178. Unavailable soil water. — As has been shown in 
a previous paragraph, free or capillary water may become 
of little use to a plant through distance, since capillarity 
is una})le to pump the water fast enough to supply ordinary 
crop needs. Water near at hand or in the immediate 
zone of the rootlet may also become unavailable through 
the obstruction of capillarity, friction instead of distance 
being the cause in this case. As the rootlet tliins the 
interstitial film at any j)oint, capillarity occurs and 
water moves toward the absorbing surface. This move- 
ment is rapid enough for plant needs until the film chan- 
nels on the particles become thin. (See Fig. 37.) As the 
zone of Ingroscopic influence of the particle is approached 



WATER OF SOIL IN ITS RELATION TO PLANTS 257 

the viscosity increases very rapidly and cuts down the 
capillarity to such a point that the needs of the plant 
are unsatisfied. Wilting therefore occurs simply be- 
cause the soil is unable to move the water rapidly 
enough for crop needs. As the viscosity of the water 
increases very rapidly after the point of lento-capillarity 
is reached, the wilting coefficient is a figure somewhat 
less than the percentage representing the lento-capillarity ; 
also, it is greater than the hygroscopic coefficient, since 
wilting due to viscosity occurs before it is possible 
for the film to become thinned to the zone of hygro- 
scopicity. Not only all the hygroscopic water is unavail- 
able, then, but also a certain small quantity of the 
capillary water lying between the point of wilting and 
the hygroscopic film. This relationship is shown by 
data from the work of Heinrich and of Briggs and Shantz ; 
men working at widely different times and under entirely 
different conditions. 



Relation of the Wilting Point to the Hygroscopic Co- 
efficient. Heinrich ^ 



Soil 


Wilting Point 


Percentage op 
Htghoscopic Water 


Coarse sandy soil 
Sandy garden soil 
Fine humous sand 
Sandy loam . . 
Calcareous soil . 
Peat .... 






1.5 
4.6 
6.2 
7.8 
9.8 
49.7 


1.15 
3.00 
3.98 
5.74 
5.20 
42.30 











' Heinrich, R. Ueber das Vermogen der Pflanzen den Boden 
an Wasser zu erschopfen. Jahresbericht der Agri.-chera., 
Band 18, Seite 368-372. 1875. 



s 



258 SOILS: PROPERTIES AND MANAGEMENT 



Relation of the Wilting Point to the Hygroscopic Co- 
efficient. BniGGs AND Shantz 1 



Soil 


Hygroscopic 
Coefficient 


Wilting Point 


Coarse sand 

Fine sand 

Fine sand 

Sandy loam 

Sandy loam .... 
Fine sandy loam . . . 

Loam 

Loam 

Clay loam 


.5 
L5 
2.3 
3.5 
4.4 
6.5 
7.8 
9.8 
11.4 


.9 

2.6 

3.3 

4.8 

6.3 

9.7 

10.3 

13.9 

16.3 



179. The wilting coefficient of plants. — It has been 
known for many years that the common plants possess 
different capacities for resisting drought. This has 
usually been ascribed to one or more of three causes : 
(1) difference in root extensions; (2) difference in ability 
to become adjusted to a slow intake of water ; and (3) dif- 
ference in pulling power against the viscosity of the water 
film. The last two capabilities would argue for different 
wilting coefficients for different crops on the same soil. 
The most extended work on this subject has been by 
Briggs and Shantz,^ who found that the permanent wilting 
point in a saturated atmosphere is practically the same 
for all plants. Later Caldwell ^ demonstrated that this 

^ Briggs, L. J., and Shantz, H. L. The Wilting Coefficient 
for Different Plants and its Indirect Determination. U. S. 
D. A., Bur. Plant Indus., Bui. 230, p. 65. 1912. 

2 Briggs, L. J., and Shantz, II. L. The Wilting Coefficient 
for Different Plants and its Indirect Determination. U. S. 
D. A., Bur. Plant Indus., Bui. 2.30. 1912. 

^ Caldwell, J. S. The Relation of Environmental Condi- 
tions to the Phenomenon of Permanent Wilting in Plants. 
Physiological Researches, Station N, Baltimore. U. S. D. A., 
Vol. I, No. 1. July, 1913. 



WATER OF SOIL IN ITS RELATION TO PLANTS 259 

relationship of the physical constants of the soil to the 
wilting point depends on the rate at which the plant 
loses water, showing that the soil factors are not entirely 
dominant in this respect. This work seemed, neverthe- 
less, to indicate that the conclusions of Briggs and Shantz 
were correct for plants of humid regions, where the wilt- 
ing occurred in a saturated atmosphere. If such is the 
case, it can be accounted for only by the fact that the 
soil forces in their effect on the wilting point are so power- 
ful as to override any distinguishing characteristics that 
the plant itself may possess, or at least reduce such an 
influence within the error of actual experimentation. 

180. Determination of the wilting point. — Briggs and 
Shantz,^ in their investigations, devised a very accurate 
method for making determinations of the wilting point. 
Glass tumblers holding about 250 cubic centimeters of 
soil in an optimum condition were used. The seeds were 
placed in this soil, after which soft paraffin was poured 
over the surface in order to stop evaporation, thus re- 
moving this disturbing factor in the capillary equilibrium 
of the moisture. The seedlings on germination were 
able to push through this paraffin. While the plants 
were developing, the tumblers were kept standing in a 
constant-temperature vat of water in order to prevent 
condensation of moisture on the inside of the glass. The 
vegetative room was under temperature control. When 
definite wilting occurred, as determined in a saturated 
atmosphere, a moisture test was made on the soil. The 
resulting figure, within ex]:)erimental error, represents 
the wilting point for the soil used. 

•Briggs, L. J., and Shantz, H. L. The Wilting Coefficient 
for Different Plants and its Indirect Determination. U. S. 
D. A., Bur. Plant Indus., Bui. 230, pp. 10-14. 1912. 



260 SOILS: PROPERTIES AND MANAGEMENT 

181. Calculation of the wilting point. — In studying 
the correlation of this wiltinjj; coefficient to soil conditions, 
Briggs and Shantz ^ advanced the following relationships. 
Expressed as formulae they represent methods of at 
least approximating the wilting point from other soil 
factors. These formulae are arranged in the order of 
their reliability, based on the data obtained by the 
authors : — 

1. Wilting point ^Moisture equivalent ^^^^^ 2.9 per cent) 

2. Wilting point ^ Hygroscopic coefficient ^^^^^ -, j p^^ ^^^^^ 

3. Wilting point 

_ Water-holding capacity (Hilgard method) - 2 1 ^^^^^ g 3 ^^^ ^^^^^^ 
2.9 

182. Relation of texture to the wilting point. — From 
the data already quoted ^ from Heinrich and from Briggs 
and Shantz regarding the hygroscopic coefficient and the 
wilting point, it is evident that a very close relationship 
exists between the texture of the soil and the percentage 
of moisture at which plants wilt. The finer the soil 
texture, the higher is the wilting point. The following 
figures, from Briggs and Shantz,^ bring out the point very 
clearly : — 

1 Briggs, L. J., and Shantz, H. L. The Wilting Coefficient 
for Difterent Plants and its Indirect Determination. U. S. D. 
A., Bur. Plant Indus., Bui. 230, pp. .56-77. 1912. 

2 This text, paragraph 178. 

3 Briggs, L. J., and Shantz, H. L. The Wilting Coefficient 
for Different Plants and its Indirect Determination. U. S. D. 
A., Bur. Plant Indus., Bui. 230, pp. 26-33. 1912. 



WATER OF SOIL IX ITS RELATION TO PLANTS 261 

Relation of Texture to the Wilting Point of Kubanka 

Wheat 



Soil 


Moisture 
Equivalent 


Wilting Point of 
Kubanka Wheat 


Sand 

Fine sand 

Fine sand 

Fine sand 

Sandy loam . . . . . 

Sandy loam 

Sandy loam 

Loam 

Loam 

Clay loam 

Clay loam 


1.55 

4.66 

5.50 

6.74 

9.70 

14.50 

18.60 

23.80 

25.00 

27.40 

29.30 


.86 

2.60 

3.33 

3.70 

4.80 

9.60 

8.84 

12.40 

13.90 

14.50 

17.10 



Briggs and Shantz have attempted to express this 
correlation by a formula which, while very inaccurate, 
shows in general the relationships already expressed. 
The correlation in this case is made between the wilting 
point and the mechanical composition of the soil : — 

Wilting point = .01 sand + -12 silt + .57 clay (error 10 

per cent) 

183. Available and super-available water. — Advanc- 
ing from the wilting, or critical, moisture content of a 
soil, all the remaining capillary water is found to be avail- 
able for normal plant use. However, when free water 
begins to appear, a condition adverse to plant growth is 
established, and as the saturation point is approached 
this condition becomes more adverse. This free water 
is designated as the super-available water, since it is 
beyond the available and its presence generates condi- 
tions unfavorable to plant growth. The upper limit of 



262 SOILS: PBOPERTIES AND MANAGEMENT 

the capillary water is called the maximum water content 
for plant growth. The bad effects of free water on the 
plant arise largely from the poor aeration that results 
from its presence. Not only are the roots deprived of 
their oxygen, but toxic materials tend to accumulate. 
Fax'orable bacterial activities, such as nitrification and 
ammonification, are much retarded also. 

The various forms of water in the soil and their avail- 
ability to the plant are illustrated diagrammatically m 
the following figure. 

HYGHOSCOPIC '%/AJT LENTOCflPILLARITY MA/IMUM Wmm 

CO[mCI£NT\ I POINT CONTINT 

HmOXOPC^KX ^OPTIMUM WATEP CONTENT \ xFREE-^JUmmmi 



/\V/MLfiBL[: MOIiTURE 



Fig. 41. — Diagram showing the forms of water in the soil and their 
relationship to the plant. 

184. Optimum moisture for plant growth. — It is 
very evident that there must be some moisture condition 
of a soil which is best for plant development. This is 
usually designated as the optimum content. It is not 
to be assumed, however, that the total range of the 
available soil water represents this condition for optimum 
plant growth. Nor is this optimum water content in 
any particular soil to be designated by a definite per- 
centage. In reality the moisture in a soil may undergo 
considerable fluctuation and yet allow the plant to de\'elop 
normally. This is because the physical condition of the 
soil changes with varying water content and the plant is 
able to accommodate itself to such a fluctuation without 
a disturbance in its normal development occurring. 
Wollny ^ has shown that the optimum moisture for com- 

' Wollny, E. Untersueliung iihcr den Einfluss der Waclis- 
thumsfaktoren auf des Produktionsvermogeu der Kultur- 



WATER OF SOIL IN ITS RELATION TO PLANTS 263 

mon field crops in general covers a range from 60 to 80 
per cent of the water capacity of the soil. Mayer ^ 
placed the optimum moisture content of wheat at 80 
per cent of the water capacity of the soil, rye at 75 per 
cent, barley at 75 per cent, and oats at from 85 to 90 
per cent. Such estimates not only emphasize the range 
of optimum moisture conditions, but at the same time 
show the relati\'ely high percentage of moisture necessary 
for maximum crop growth. 

Granulation has considerable influence on the range of 
optimum moisture conditions, since the better the granu- 
lation, the better is the soil able to accommodate itself 
to changes in water content without disturbance of 
plant growth. The poorer the tilth of any soil, the 
narrower does this fluctuating in optimum moisture be- 
come. In moisture conservation and control a granular 
soil is one of the first improvements to be aimed at. 
Drainage, liming, addition of organic matter, and tillage, 
by leading up to such a condition, increase the effective- 
ness and economv of utilization of soil moisture. 



pflanzen. P'orseh. a. d. Gebiete d. Agri.-Physik, Band 20, 
Seite .53-109. 1897. 

1 Mayer, A. Uber den Einfluss kleinerer oder Grosserer 
Mengen von Wasser auf die Entwickelung einiger Kultur- 
pflanzen. .Jour. f. Landw., Band 46, Seite 167-184. 1898. 



CHAPTER XIII 



THE CONTROL OF SOIL MOISTURE 



In the discussion of the water requirements of phmts, 
it was apparent that for a normal yield of any crop the 
amount used by the plant alone was very great, varying 
from five to ten acre inches according to conditions. Were 
this the only loss of water, the question of raising crops 
with given amounts of rainfall would be a simple one. 
Three further sources of water loss, however, are usually 
found functioning in the soil and tending to lower the 
water that would go toward transpiration, a loss absolutely 
necessary for proper plant growth. The various ways by 
which water finds an exit from a soil are (1) transpiration, 
(2) run-off over the surface, (3) percolation, and (4) evap- 
oration. The following diagram makes clear their re- 
lationships. 



Transpimtion 



TraniOirat/on,^ 




Fig. 42. — Diagnuu illustrating the ways bj' which water may be lost 

from a soil. 

264 



THE CONTROL OF SOIL MOISTURE 265 

It is immediately obvious that as the losses by run-off, 
leaching, and evaporation increase, the amount of water 
left for crop utilization decreases. In arid and semiarid 
regions this is fatal to plant growth, while in humid regions 
it may be such a factor in periods of drought as to se- 
riously reduce the harvest. Control of moisture is there- 
fore necessary in all regions, and this really consists in 
so adjusting run-off, leaching, and evaporation as to 
maintain optimum moisture conditions in the soil at all 
times. This control should result in a proper and eco- 
nomic utilization of the soil water by the plant. 

185. Run-off losses. — In regions of heavy rainfall 
or in areas where the land is sloping or rather impervious 
to water, a considerable amount of the moisture received 
as rain is likely to be lost by running away over the sur- 
face. Under such conditions two considerations are im- 
portant : (1) by not entering the soil the water is lost for 
plant use ; and (2) washing of the soil may occur, which 
if allowed to proceed may entirely ruin the land. The 
amount of run-off varies with the rainfall, the slope, and 
the character of the soil. In some regions it may rise 
as high as 50 per cent of the rainfall, while in arid regions 
it is of course very nearly zero. As a general thing, this 
loss is estimated with the losses by leaching, the two being 
expressed as one figure. 

186. Percolation losses. — When at any time the 
amount of rainfall entering a soil becomes greater than 
the water-holding capacity of the soil, losses by percola- 
tion will result. The losses will depend largely on the 
amount and distribution of the rainfall and the capa- 
bility of the soil to hold moisture. The bad effects of 
excessive percolation are twofold : (1) the actual loss of 
water, and (2) the leaching-out of salts that may function 



266 SOILS: PROPERTIES AND MANAGEMENT 

as plant-food. The quantity of nutrient elements lost 
aniuially from the average soil in a humid region more 
than equals that withdrawn by the crops. The results 
from the Rothamsted drain gauges' from 1871 to 1904 
on a clay loam soil of three different depths are inter- 
esting as to the light that they afford regarding actual 
drainage losses : — 













Proportion of 






Drainage through 


Rainfall Drained 








u>\jii^ 




through Soil 




Rain- 
fall 












Depth in Inches 


Per Cent 




20 


40 


60 


20 40 ' 


60 

84.5 


January .... 


2.32 


1.82 


2.05 


1.96 


78.5 88.4 


February . 






1.97 


1.42 


1.57 


1.48 


72.2 80.0 75.2 


March . . 






1.83 


0.87 


1.02 


0.95 


47.6 55.6 52.0 


April . . 






1.89 


0.50 


0.57 


0.53 


26.5 30.0 28.0 


May . . 






2.11 


0.49 


0.55 


0.50 


23.2 26.1 23.6 


June . . 






2.36 


0.63 


0.65 


0.62 


24.0 27.6 26.3 


July . . 






2.73 


0.69 


0.70 


0.65 


25.3 25.6 23.8 


August . . 






2.G7 


0.62 


0.62 


0.58 


23.2 23.2 21.7 


September 






2.52 


0.88 


0.83 


0.76 


35.0 32.8 30.0 


October 






3.20 


1.85 


1.84 


1.68 


57.8! 57.5 


52.5 


November . 






2.86 


2.11 


2.18 


2.04 


76.7 


76.3 


72.4 


December . 




ear 


2.52 


2.02 


2.15 


2.04 


80.3 


85.4 


81.0 


Mean total per j 


28.98 


13.90 


14.73 


13.79 


48.2 


51.0 


48.0 


Winter, October to 
















March . . . . 


14.70 


10.09 


10.81 


10.15 


68.6 


72.8 


69.0 


Summer, April to 
















September . . . 


14.28 


3.81 


3.92 


3.64 


26.6 


27.4 


25.4 



The rainfall and relative loss through the 40-in('h depth 
of soil is shown graphically in the followmg diagram : — 



1 Hall, A. D. The Book of the Rothamsted Experiments, 
23. London. 1905. 



THE CONTBOL OF SOIL MOISTUBE 



267. 





















/ 


^ 






N. 




Qy^/nf 


4LL^ 


^ 


/ 






/ 


N 

^ 


^ 




\ 
\ 


* 




J> 










/ 








s 














/ 










\ 














/ 










\ 














/ 












^e^ii 






















\ 










A 












\ 





'" 






^ 









Fig. 43. — Rainfall and percolation losses through a 40-inch soil column. 
Lj-simeter records, Rothamsted Experiment Station, England. 

It appears from these figures that about 50 per cent 
of the rainfall in such a climate as that of England is 
lost by percolation alone. It appears also that the loss 
is much lower in summer than in winter, the ratio being 
about one to three. Also, the longer the soil column, 
the less is the percolation, due to the greater water- 
holding capacity possessed by the longer column. 

187. Methods of checking loss by run-off and leaching. 
— It must not be inferred that the soil is never in such 
a condition that percolation, and even run-off, are not 
advantageous. Often in winter the excess water may 
be drained over the surface with no damage whatsoever. 
Also, when the soil becomes filled with free water, either 
in winter or in the growing season, drainage must 
take place in order to establish optimum soil conditions. 
The control of the free water of the soil may be brought 



268 SOILS: PROPERTIES AND MANAGEMENT 

about by drainage operations or by methods that will 
increase the water-holdinjj; capacity of the soil. The 
former is really a matter of engineering technique and 
will be treated in a separate chapter. The latter is a 
fimction of the soil itself and must be specifically con- 
sidered at this point. 

The necessity of giving attention to losses due to 
run-off and leaching varies with climatic conditions. 
In very humid regions these losses are of grave importance, 
while in arid regions they are insignificant as compared 
with losses by evaporation. For example, in P^ngland 
the losses by percolation and run-off in many cases are 
as high as 60 per cent of the rainfall. In the Mississippi 
River basin the loss is 50 per cent, in the Missouri it is 
about 20, while in the Great Basin it drops to zero. This 
does not indicate that drainage is not practiced in the 
last-named region, however, for, owing to over-irrigation, 
seepage, and other conditions, drainage operations often 
become as important as in humid climates. 

The quantity of water entering a soil is determined 
almost entirely by the physical condition of the soil. 
If the soil is loose and open, the water enters readily and 
little is lost over the surface as run-off. If, on the other 
hand, the soil is compact, imper\ious, and hard, most 
of the rainfall runs away, and not only is there a serious 
loss of water, but considerable erosion may also result. 
The first step in checking run-off losses, therefore, is 
strictly physical in nature. As the water that has entered 
the soil moves downward it is continually being changed 
to capillary water in its passage. If the capillary capacity 
of the soil is high, a greater percentage of this rain water 
becomes capillary and a less percentage is left to be carried 
away as gra\itational water. The secret in the control 



THE CONTROL OF SOIL MOISTURE 269 

of run-off aiul percolation, then, is first, to have a loose, 
open structure of soil in order to facilitate ready entrance 
of the water ; and secondly, to promote and encourage 
a physical condition of soil which provides high capillary 
capacity. Drainage, lime, humus, and good tillage en- 
courage granulation, which has so much to do with the 
proper entrance of water into the soil and its proper 
handling and utilization therein. The benefits of drain- 
age are felt only when free water, superavailable to 
plants, becomes present. Its quick removal, therefore, 
not only betters the physical condition of the soil, but 
also aids in the maintenance of the optimum moisture 
conditions for the plants. 

Fall and early spring plowing is always recommended 
as a means of increasing the moisture capacity of the 
soil, particularly where organic matter is well supplied. 
It provides a deep soil, and should establish the best 
conditions for the storage of moisture, as well as food, 
for the plant. If organic matter is not supplied, deep 
plowing is not advisable on light sandy soil ; but on 
clay soil it is beneficial because of the loosening and granu- 
lating effect. Fall plowing in particular is to be recom- 
mended for such soil, as the loose condition produced 
facilitates the entrance of surface water while the granu- 
lation that the soil undergoes during the winter increases 
its water-holding power. A soil in excellent physical 
condition may contain considerably more water than 
the soil of the same texture but in poor tilth, and yet 
present better conditions for crop growth. Where fall 
plowing cannot be done, early spring plowing is the next 
best procedure. 

188. Evaporation losses. — Evaporation of soil water 
takes place almost entirely at the surface, exceptions 



270 SOILS: PROPERTIES AND MANAGEMENT 

being where deep, large cracks occur, which allow thermal 
loss directly from the subsoil. This loss of water by 
direct evaporation from the soil may be excessive and 
may result in direct reduction of the crop yield — a type 
of loss so familiar that examples hardly need be cited. 
In the results with the Rothamsted rain gauges about 
50 per cent of the annual rainfall was regamed in the 
drainage water. Since the gauges bore no crop, the 
remaining 50 per cent must have been lost by evapora- 
tion. It should be noted that in the summer months 
under warm temperature this loss was greatest, amount- 
ing to 75 per cent of the rainfall. Correspondingly, in 
the semiarid and arid sections of the country, where 
there is little or no drainage, the rainfall is all lost by 
evaporation. Investigations indicate that about 70 per 
cent of the precipitation on the land surface is derived 
from evaporation from land surface. Even in humid 
regions, where the annual rainfall is ample for maximum 
crop production, the crops are frequently reduced below 
the profit point by prolonged periods of dry weather in 
the growing season, during which the loss of water from 
the plants, coupled with the loss from the soil, exhausts 
the moisture supply. 

While run-off and percolation are directly proportional 
to the rainfall, loss by evaporation does not vary to such 
a degree. The loss by percolation depends almost 
directly upon the amount of rainfall above the retentive 
power of the soil. In years of heavy precipitation, 
losses by percolation must increase. Evaporation from 
the soil depends largely upon the time that the soil 
surface is moist, and this will not vary markedly from 
year to year. The following figures from the Rothamsted 
drain gauges may be quoted in this regard : — 



THE CONTROL OF SOIL MOISTURE 
Records from Rothamsted (1870-1878) '■ 



271 



Rainfall Inches 


Evaporation Inches 


Percolation Inches 


22.9 


17.3 


5.6 


26.3 


18.4 


7.9 


29.3 


18.1 


11.2 


30.8 


18.3 


12.5 


31.6 


16.6 


15.0 


32.6 


18.0 


14.6 


34.2 


18.0 


16.2 


35.8 


18.3 


17.5 


42.7 


17.2 


25.5 



A rough calculation may be made which will show the 
apportionment of the yearly rainfall in a humid region of 
the temperate zone between the three forms of losses — 
run-off and percolation, evaporation, and transpiration. 
The percolation under a rainfall, say, of 28 inches, as 
shown by the Rothamsted work, is roughly 14 inches, or 
50 per cent. The water requirement of an ordinary 
crop is about 7 inches. This leaves a loss of 7 inches 
to be credited to evaporation. In other words, one- 
half the rainfall goes as run-off and percolation, while 
the other half is divided about equally between the plant 
and loss by evaporation. While run-off and percolation 
may be checked to some extent, not enough conservation 
can occur in this direction to tide a crop over a period 
of drought. Paramount attention should therefore be 
directed toward the checking of losses by evaporation, 
since moisture thus saved means just that amount added 
to the water available for crop use. It should be remem- 
bered that over a large proportion of cultivated lands 



1 Warington, R. 
1900. 



Physical Properties of the Soil, p. 109. 



272 SOILS: PROPERTIES AND MANAGEMENT 

the crop yields are controlled more directly by lack than 
by excess of water. It is a common observation that 
soils which ordinarily give a low yield in seasons of nor- 
mal or low rainfall give good yields in a wet season, 
indicating how dominant is this influence of moisture on 
soil fertility. 

189. Methods of checking evaporation losses. — All 
methods for the reduction or elimination of evaporation 
losses depend on one or both of two functions: (1) the 
actual control of evaporation as it occurs at the surface ; 
and (2) the prevention of the movement of capillary 
water upward to take the place of the moisture already 
lost. It has been shown that as water is lost at the sur- 
face of a soil, movement is induced and capillarity is 
set up. Such action, if allowed to continue, must ulti- 
mately bring about great losses. The obstruction of 
capillarity would obviously lower these losses to a marked 
degree. As it is difficult and often impracticable to en- 
tirely eliminate evaporation, the most successful methods 
of water control usually include a change in the structural 
condition of the soil which tends toward a lower capil- 
larity, especialh' at the surface. Of all the methods of 
moisture conservation, the use of a mulch has been found 
most satisfactory. The consideration of mulches is 
therefore one of the most important phases in the study 
of moisture control. 

190. Mulches for moisture control. — Any material 
applied to the surface of a soil primarily to prevent loss 
by evaporation may be designated as a mulch. It may 
at the same time fulfill other useful functions, such as 
the keeping down of weeds and the maintaining of a 
uniform soil temperature. By the conservation of the 
moisture, more water remains in the soil for the solution 



THE CONTROL OF SOIL MOISTURE 273 

of the essential elements, and bacterial activity is en- 
couraged. As a general rule, more soluble plant-food is 
likely to be found under a mulched soil, other conditions 
being equal, than under a soil not so treated. 

191. Kinds of mulches. — ^Mulches are of two general 
sorts, artificial and natural. In the former case, foreign 
material is merely spread over the soil surface and evapora- 
tion is obstructed thereby. Manure, straw, leaves, and 
the like, may be used successfully. Such mulches, while 
very effective, are not generally applicable to field crops 
where intertillage is practiced, since they would make 
cultivation absolutely impossible by cumbering the soil 
surface with a large amount of inert material. Their 
use is therefore limited to intensive crops such as are 
found in trucking operations. Leaves, including pine 
needles, and sawdust are very effective as a mulch, but 
some precautions should be observed in their application. 
For example, the oak is rich in tannic acid, which may 
be washed out of the mulch into the soil and by its effect 
on the growing plant may cause a lowering of productivity. 
In some European countries, as well as in a few localities 
in America, stones have been drawn on the soil to serve 
as a mulch, particularly in orchard and vineyard culture, 
with markedly beneficial effects. Particularly is this 
true on such lands as are too steep to permit cultivation. 
As further evidence of the utility of this practice, it has 
been observed in the fruit-growing section of the Ozark 
Mountains, and doubtless in other regions, that the 
removal of stones from the land not only results in the 
soil's becoming harder, but also reduces crop yield by 
increasing loss of moisture. It is therefore necessary 
for the farmer to decide whether the inconvenience 
to tillage or other operations due to the presence of 



o 



274 SOILS: PROPERTIES AND MANAGEMENT 

stones may not be more than offset by their beneficial 
effects. 

The materials for mulching mentioned above are all 
strictly artificial, and their application is greatly limited, 
due to the lack of material and the expense involved. 
They are therefore used only under special conditions. 
The second type of mulch is almost universal in its prac- 
tical availability. 

By proper cultivation almost any soil surface may be 
brought into such a condition that evaporation of mois- 
ture is more rapid than the upward capillary movement. 
This is because surface tillage produces a loose, open 
structure, which, while increasing the rate of thermal 
movement of the water, at the same time obstructs 
capillary action. The surface layer, therefore, quickly 
becomes air-dry and is in a condition designated as a 
soil mulch. As it differs from the soil below only in 
structure, it has numerous advantages over artificial 
mulches, at the same time performing successfully all 
the functions of the latter. Since not only the water in 
the mulch is sacrificed but also a small quantity pumped 
upward by capillarity during the operation, speed in 
formation is of importance. The tillage implements 
that give the maximum looseness and granulation will 
prove the most successful. A spike-tooth harrow or a 
weeder is the instrument ordinarily employed. 

192. The functions of a mulch. — A soil mulch depends 
for its effectiveness on two functions — (1) the shiitting- 
off of evaporation, and (2) the checking of capillary move- 
ment upward. It has already been shown that thermal 
movement of water through dry soil layers is practically 
nil ;^ therefore, as long as the soil is dry, evaporation is 

' This text, paragraph 166. 



THE CONTROL OF SOIL MOISTURE 275 

very low. Moreover, any layer of air-dry soil resists 
wetting, principally because of the resins and oils that 
become deposited on the surface of the soil particles. 
This material, called " agricere," has a low surface tension 
and the capillary water film is not easily resumed under 
such conditions. Again, if the soil is well granulated 
it is able to assume a looser and more open structure. 
The interstitial angles, which afford spaces for capillary 
surfaces, are cut down, and the capillary pulling power 
of the layer is much reduced even if it should assume a 
film of water. It is evident that looseness and dryness 
are the essentials in the efficiency of a soil mulch. As 
long as a mulch is dry, texture is not a very important 
factor in efficiency, a dry sand being about as effective 
as a dry clay. Texture is important, however, in the 
length of time that a mulch will remain effective. Due 
to the fact that the capillary power of a clay is so great, 
it will become moist from below after a few days ; while 
a sand mulch, if there is no rain, will remain dry for an 
indefinite period. On a heavy clay soil in fine tilth a 
mulch m^y be destroyed by moist, foggy weather, or 
by a number of days of very humid atmosphere ; such a 
condition, by causing condensation of moisture on the 
clay, hastens the reestablishment of capillarity with the 
subsoil, thus allowing moisture to be pumped up and 
lost. 

193. The soil mulch versus the dust mulch. — A few 
words will not be amiss at this point regarding the term 
" dust mulch," which is observed so commonly in soil 
literature. This term would indicate that the mulch is 
in a very fine condition, its granulation having been 
broken down. Such a condition would not be conducive 
to efficiency, as it would encourage capillarity, while at 



276 SOILS: PROPERTIES AND MANAGEMENT 

the same time it would become puddled on wetting — 
certainly a very undesirable condition. As a matter of 
fact, efficient mulches are not in a dust form, but are 
granulated and much looser than could be obtained were 
they finely divided. It is evident that the term " dust 
mulch " is incorrect and should be superseded by " soil 
mulch," a figure of speech which more exactly expresses 
the true field conditions. 

194. Formation of a mulch. — It has already been 
stated that a mulch should be formed as quickly as 
possible. This would not be such a factor were the 
mulch adjusted only once in a season. It is necessary, 
however, especially in humid regions, to re-form a mulch 
every week or ten days. The cutting-down of formation 
losses therefore becomes important. In general the 
mulch should be made just as soon after a rain as it is 
possible to work the land, since the most rapid evapora- 
tion occurs during the few hours immediately after a 
rain, when the soil is very moist. Even after light showers 
the soil should be quickly cultivated, since the rain may 
have established a capillary communication with the 
surface and thus provided for a rapid loss of the water 
already conserved by previous work. Under arid con- 
ditions, where the atmosphere is dry and hot and in free 
circulation, the surface soil is quickly dried out after a 
rain. This drying takes place so rapidly that the capil- 
lary films quickly become so thin that movement is 
stopped and no more water is brought to the surface. 
The soil may be ever so hard and compact, but as long 
as it is kept dry it very effectively conserves the moisture 
below. The more rapid the loss, the more quickly will 
the mulch condition be created, and therefore the less the 
total loss of water is likely to be. This has been demon- 



THE CONTROL OF SOIL MOISTURE 



277 



strated by Buckingham ^ in some experiments in which 
arid climate conditions were created at the surface of a 
capillary column forty-six inches in height. The soil 
was a fine sandy loam. At first the loss of water under 
the arid conditions was very rapid and exceeded that 
under the humid conditions; but the rate of loss soon 
dropped considerably below that of the humid column, 
and continued to fall behind during the twenty days 
of the experiment. The differences in this case were 
due to self-mulching, a very common phenomenon of 
arid land soils, particularly those of a loamy character. 
This self-mulching is often seen in sands in humid 
regions. The under layers of a sand pile are always 
moist, due to the self-mulching tendencies of the sur- 
face. The results of Buckingham are shown in the fol- 
lowing curves : — 



1 


200 






^ 


/iUMID 




/oo 






-^ 


ARID 




A 


^ 











/O IS ZO OA>Y<S £L/IPS£a 



Fig. 44. — Evaporation curves on a sandy loam under humid and arid 
conditions. Self-mulching has occurred under the arid conditions 
and a reduction in evaporation has resulted. 



1 Buckingham, E. Studies on the Movement of Soil Mois- 
ture. U. S. D. A., Bur. Soils, Bui. 38, pp. 18-24. 1907. 



278 SOILS: PROPERTIES AND MANAGEMENT 

195. Depth of a mulch. — The depth of a mulch is an 
important question in humid regions. Not only must 
all the water in the layer be sacrificed in order to make 
the mulch effective, but the plant-food of that layer 
is temporarily withdrawn from use. In humid areas, 
where the surface soil is usually not over eight or ten 
inches in depth, the latter consideration is vital, since 
the fertility of the soil would be greatly depressed by a 
deep soil mulch. Another factor to be considered here 
is the possible root pruning that may occur while the 
nuilch is being formed. While not of importance early 
in the season, it is worthy of considerable attention when 
the intertilled crop attains some age. It has been shown, 
with such crops as corn, that considerable depression in 
yield may result from the maintenance of a mulch at too 
great a depth, some of the feeding roots being cut off 
thereby. For such reasons the average depth of mulch 
for humid regions and in dry-farming operations has 
become regulated to about three inches, although in the 
late cultivation of corn a less depth than this is advocated. 
In irrigated regions where little rainfall occurs and where 
the soil is very deep and uniformly fertile, mulches as 
deep as ten or twelve inches are sometimes found, es- 
pecially in orchards. As rainfall occurs but few times 
during the season, such a mulch often needs no attention 
except for its original formation. With crops ha\ing 
shallow roots a thinner mulch layer must of course be used. 

196. Resume of mulch control. — To summarize briefly-, 
the cardinal points in mulch control are: (1) mulches are 
more effective and more easily maintained in an arid than 
in a humid climate ; (2) their efficiency depends directly 
on their dryness, looseness, and granulation ; {'.^) sandy 
soil is more easilv maintained as a mulch than clay soil ; 



THE CONTROL OF SOIL MOISTURE 



279 



(4) from two to three inches is ordinarily the most effec- 
tive depth ; (5) after a heavy rain, the soil mulch must 
be renewed by tillage, and this is much more urgent on 
clay than on sandy soil ; even without rain, a clay mulch 
may become inefficient ; (6) tillage for mulch purposes 
must ordinarily be more frequent m spring or during 
periods of heavy rain, than at other times of the year; 
(7) the use of foreign materials as mulches may be justi- 
fied under special circumstances. 

197. Water saved by a mulch. — It is very difficult 
to quote data regarding the capacity of a mulch to con- 
serve moisture, since conditions vary to such a degree 
from one region to another. Again, water may not be the 
limiting factor in crop growth, and even if moisture were 
saved there might be but little influence on crop yields. 
As a general rule, mulches are most easily maintained 
and most effective in arid and semiarid regions. Since 
there is no doubt that moisture, under such conditions, is 
the limiting factor in plant growth, data from such regions 
should be especially significant. 

Moisture Content of Mulched and Unmulched Eastern 
Montana Soils. Average of Three Years. ^ October 6 



Unmulched 




First foot . 
Second foot 
Third foot 
Fourth foot 
Fifth foot . 
Average 



1 Buekman, H. O. Moisture and Nitrates in Dry Land 
Agriculture. Proc. Amer. Soc. Agron., Vol. 2, p. 131. 1910. 



280 soils: properties and management 

If the wilting' point of this soil is per cent, the mulched 
area contains more than twice as much available moisture. 
This 3.8 per cent of available moisture by which the 
mulched soil excels the unmulched is equivalent in a five- 
foot depth to about 250 tons of water, enough to increase 
the crop by a ton of dry matter — certainly not an insig- 
nificant sa\'ing where crop yield and moisture are so very 
closely correlated. 

A considerable amount of experimentation ^ is available 
which seems to indicate that mulching a soil does not in- 
crease its yield over a soil not so treated. One reason for 
this, as already suggested, may be in the fact that water 
may not have been the limiting factor, the rainfall having 
been just right in amount and distribution. Again, the 
roots may have so intercepted the capillary water as to 
have allowed no more evaporation from the immulched 
soil than from the mulched. In some soils hard layers 
often form w^hich act in repelling capillary movement. 
Such a condition would function as successfully in check- 
ing losses as if a true mulch were present. In the study 
of mulches and their value in increasing a crop, decided 
opinions should not be advanced until every phase has 
been thoroughly investigated regarding the exact factors 
dominant in the determination of yield. The extended 
use of soil mulches in the Corn-Belt and in dry-farming 
operations argues for their benefits. 

198. Effect of mulches other than on moisture. — That 
mulching a soil has other effects besides the conserving of 
moisture is universally evident. In general the physical 
condition of the soil is always better after a crop that has 

' Gates, J. S., and Cox, H. R. The Weed Factor in the 
Cultivation of Corn. U. S. D. A., Bur. Plant Indus., Bui. 
257. 1912. 



THE CONTROL OF SOIL MOISTURE 



281 



been intertilled. Xot only has the surface been kept 
well granulated, but the presence of optimum moisture 
below has allowed the granulating agents to become 
more active. The following of potatoes by corn is, at 
least partially, an attempt to take advantage of the 
better tilth of the soil with a crop that is particularly 
benefited thereby. Again, a mulch not only tends to 
allow a ready entrance of water into the soil, but at the 
same time increases the water-holding capacity — factors 
already emphasized in the discussion of control of losses 
by percolation and run-off. By keeping down weeds ^ 
another saving is effected, not only in moisture but also 
in plant-food. Some results from an experiment - con- 
ducted at Cornell University serve to illustrate the re- 
lation of mulches and weeds to soil moisture and crop 
production in a humid region in a season of good rainfall. 
The crop grown was maize. Every third plot was a 
check and was given normal treatment : — 



Cheek plot 

Weeds removed, but not cultivated . 

Mulched with straw 

Check plot 

No cultivation ; weeds allowed to grow 
One cultivation ; weeds allowed to 

grow 

Check plot 



Yields Calcu- 
lated TO Basis 

OF 100 ON 

Check Plots 



Soil Moisture 

DURING August 

Per Cent 




17.0 
17.7 



1 Cates, J. S., and Cox, H. R. The Weed Factor in the Culti- 
vation of Corn. U. S. D. A., Bur. Plant Indus., Bui. 257. 1912. 

- Craig, C. E. The Cause of Injury to Maize by Weeds. 
Presented as a thesis for the degree of M. S. A., Cornell Uni- 
versity. Unpublished. June, 1908. 



282 SOILS: PROPERTIES AND MANAGEMENT 

The application of a soil mulch is not confined to 
intertilled crops such as maize, potatoes, vineyards, 
fallow, and the like. I nder some conditions it may be 
applied to grain fields with good results. In those sections 
of the country where dry farming is practiced, it is not 
uncommon to drag the grainfield with a sharp-tooth 
harrow, the teeth pointing backward. This is begun when 
the plants are small, and may be continued until they 
attain a considerable size or until they sufficiently shade 
the ground to greatly reduce surface evaporation. 

199. General usefulness of a mulch. — While a soil 
mulch is used primarily in order to conserve moisture, 
its relationships are different in different regions accord- 
ing to climatic and cropping peculiarities. In dry- 
farming regions a mulch is maintained as nearly as possible 
the year round, since moisture must be carried from the 
previous summer and winter to the growing season in 
order to supplement the rainfall occurring at that time. 
In irrigated regions a mulch is useful in two ways — by 
conserving the rainfall and by checking the loss of irriga- 
tion water ; after the latter is once in the soil less addi- 
tional water need be applied and the consequent cost of 
irrigation is much less. Again, in arid regions where 
there is an excess of soluble salts, rapid evaporation is 
detrimental since these salts tend to concentrate near 
the surface and become harmful to plants. The ])re- 
vention of the rise of alkali is therefore a very important 
function of the soil mulch in such regions. 

In humid regions the utilization of a soil mulch is 
much less intense, since the conservation of moisture 
over long periods is unnecessary, due to the rainfall. 
However, during tlie growing season periods of drought 
occur, when if available water is lacking in the soil, the 



THE CONTROL OF SOIL MOISTURE 283 

crop suffers. The amount of moisture conserved by a 
mulch will usually keep the plant growing normally 
through such periods, while crops on soils not so treated 
may suffer greatly. The tiding of crops over short periods 
of light rainfall is the chief function of mulches in humid 
climates. 

200. Other practices affecting evaporation losses. — 
Although the control of water by mulches is such an 
important consideration, other means of checking losses 
are available. These may be grouped under five heads : 
(1) fall and early spring plowing, (2) rolling, (3) shelters, 
(4) level cultivation, (5) plants. 

201. Fall and early spring plowing. — Fall and early 
spring plowing owe much of their efficiency to the con- 
servation of moisture effected through the creation of a 
mulch over the surface. Fall plowing may be practiced 
for a number of reasons, but in regions of deficient rain- 
fall, particularly in winter, the conservation of the mois- 
ture in the soil at the close of the growing season is an 
important consideration. This practice is well adapted 
to those soils in semiarid sections that do not blow too 
badly when fall-plowed, and where the winter rain is 
not sufficient to saturate the soil. If the soil is left in 
the bare, hard condition resulting from the removal of 
a crop of maize, wheat, or barley, a large quantity of 
water may be lost by evaporation during the fall months. 

For the average farmer in humid regions where the 
winter rainfall is sufficient to saturate the soil, early 
spring plowing, coupled with tillage, is very important. 
Not only may moisture be conserved, but the soil is 
worked at the stage when it yields most readily to pul- 
verization. Fallow land, and bare stubble land of fine- 
textured soil, are most benefited, since they become 



284 SOILS: PROPERTIES AND MANAGEMENT 

compact to the very surface as a result of the winter 
rain and snow, and are therefore in condition for the 
most rapid loss of water. They should be plowed as 
early as practicable without injury to their structure. 
At the Wisconsin Experiment Station ^ two adjacent 
pieces of land very uniform in character were plowed 
seven days apart. At the time when the second plot 
was plowed, it was found to have lost 1.75 inches of 
water from the surface four feet in the previous seven 
days ; while the piece plowed earlier had actually gained, 
doubtless by increased capillarity, a slight amount of water 
over what it had contained when plowed. There was a 
conservation of nearly two inches of water in the root zone 
as a result of plowing one week earlier — enough to 
produce 1500 pounds of dry matter in maize to the acre, 
if properly utilized. 

202. Rolling. — Very often in the spring, when the 
seed bed is very loose, rolling is resorted to, in order to 
bring about a compaction of the soil. At the same 
time capillarity is established with the firmer earth 
beneath, and as the moisture moves upward a rapid 
germination of the seed is induced. Care must be taken 
that this capillarity be checked once it has performed 
this office, as great losses from evaporation may occur 
at the surface and the crop be robbed of much available 
water. It is an economic procedure in such cases to 
follow the roller after a few days with a harrow, in order 
that a mulch may be established and this loss checked. 

203. Shelters. — Shelters of any kind, whether natural 
or artificial, tend to break the wind velocity and thereby 
check losses by evaporation. Strips of timber are com- 

1 King, F. II., The Soil, p. 189. New York. 1906. 



THE CONTROL OF SOIL MOISTURE 285 

monly grown or retained for this purpose. Wooden fences 
and walls of one sort or another have a similar effect. 
Windbreaks composed of growing plants have the dis- 
advantage that for a considerable distance beyond the 
spread of their branches their roots penetrate the soil 
and use the moisture, which is one reason for the smaller 
growth of crops near trees. Bearing on the efficiency of 
windbreaks, results by King ^ show that when the rate 
of evaporation at twenty, forty, and sixty feet to the 
leeward of a black oak grove fifteen to twenty feet high 
was 11.5, 11.6, and 11.9 cubic centimeters, respectively, 
from a wet surface of twenty-seven square inches, the 
evaporation was 14.5, 14.2, and 14.7 cubic centimeters, 
at two hundred and eighty, three hundred, and three 
hundred and twenty feet distant — or 24 per cent greater 
at the outer stations than at the inner ones. A scanty 
hedgerow reduced evaporation 30 per cent at twenty 
feet and 7 per cent at one hundred and fifty feet, below 
the evaporation at three hundred feet from the hedge. 

Very often tent shelters are used in the growing of 
tobacco. The commonest form of the tent is a frame 
eight or nine feet high, over which is spread a loosely 
woven cloth. Investigations by Stewart ^ in Connecticut 
showed : (1) That the tent greatly reduced the velocity 
of the wind. This reduction amounted to 93 per cent 
when the outside velocity was seven miles an hour, and 
85 per cent when the outside velocity was twenty miles 
an hour, there being a small regular decrease in relative 
efficiency with increased velocity of the wind. (2) The 
relative humidity under the tent was higher than outside, 

1 King, F. H. The Soil, p. 205. New York. 1906. 

2 Stewart, J. B. Effects of Shading on Soil Conditions. 
U. S. D. A., Bur. Soils, Bui. 39. 1907. 



286 SOILS: PROPERTIES AND MANAGEMENT 

and during a good part of the time attained a difference 
of 10 per cent. The effect of this was to reduce evapora- 
tion by from 53 to 63 per cent on different days in July, 
in spite of a higher temperature inside the tent. (3) The 
direct effect of this was to increase the moisture content 
in the soil in spite of a larger crop growth under the tent. 
These differences are shown by the following curves (see 
Fig. 45), which represent the percentage of water in the 
soil to a depth of nine inches from June 13 to August 1. 



ie 


e> 


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IS io es- JO ss 


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Fig. 45. — Curves showing the percentage of moisture in a sandy soil to 
the depth of nine inches inside and outside of a loosely woven tent 
over a period of about fifty days. Heavy line, moisture inside of 
tent ; broken line, moisture curve of soil outside of tent. 



Not only was the tent effective in preventing evapora- 
tion and thereby increasing the average moisture content 
of the soil, but the soil was able to maintain a more uni- 
form content, due to the freer movement and adjustment 
of the capillary water under the tent — conditions more 
conducive to rapid crop growth. 

204. Level cultivation. — The \elocity of the wind 
next to the ground may be checked by ridging the soil. 
It is doubtful whether this practice conserves moisture, 



TflE CONTROL OF SOIL MOISTURE 287 

because a greater amount of surface is exposed over 
which evaporation may take place. On the other hand, 
wide experience, as well as investigation, indicates that, 
for the conservation of water, level culture is better than 
ridged culture. This principle has led to the gradual 
abandonment of the practice of " laying by " corn and 
potatoes with a high ridge. In all regions of deficient 
rainfall, the best practice prescribes level tillage and a 
fine, dry mulch, both of which are attained by the frequent 
use of shallow-running small-tooth cultivators. Many 
experiments have demonstrated the larger crop yields 
to be obtained, on the average, from this practice. 

205. Plants. — Plants growing on the soil tend to 
check evaporation from two causes — (1) their shading 
effects, and (2) the tendency of the roots to intercept 
capillary water as it moves upward and to appropriate 
it for plant growth. Plants, however, tend to intercept 
a certain amount of rain and prevent its ever reaching 
the soil. The amount of water wasted in this way by 
forests ranges from 15 to 30 per cent. In general this 
tendency just about offsets the saving that occurs from 
shading. 

206. Summary of moisture control. — It is clearly seen 
from the discussion of moisture control that the structural 
condition of the soil is the secret of successful operation. 
Run-off and leaching are reduced by increased capillary 
capacity, a structural relationship. Evaporation is 
checked by a soil mulch, which depends for its effective- 
ness on its physical condition. Drainage, lime, addition 
of organic matter, and tillage in perfecting granulation 
function in increasing the ease and effectiveness with 
which soil moisture may be controlled. It must be 
clearly kept in mind that all such control is directed 



288 SOILS: PROPERTIES AND MANAGEMENT 

toward the regulation of the soil moisture in such a way 
that an optimum water supply may be held constantly 
in the soil during the growing season. If this can be 
accomplished, the largest crop yields may be expected that 
are possible under the existing fertility conditions of any 
soil. 



CHAPTER XIV 
SOIL HEAT^ 

Normal plant growth is practically suspended below a 
temperature of about 40° F., while proper germination of 
seeds does not proceed much below that temperature. 
As a rule it is not desirable to place either seeds or plants 
in a soil in which active growth does not take place almost 
immediately, since certain molds and fungi, active at 
low temperature, may sap their vitality and ultimately 
cause their destruction. The desirable chemical reactions 
in the soil are checked to a certain extent by lack of heat, 
while the important biological activities are greatly im- 
peded, if not brought entirely to a standstill, when the 
soil temperature approaches 32° F. Such functions as 
the decay and putrefaction of organic matter, the forma- 
tion of ammonia from simple humic bodies, the building-up 
of this ammonia into the nitrate form, and the fixation 
of the free nitrogen either by free-fixing or symbiotic 
bacteria, depend on an optimum soil temperature. 

A knowledge of the functions of heat, therefore, es- 
pecially as to its relationship to plant growth and bac- 
terial activities, becomes important ; for the farmer can 
to a certain extent control soil temperature. He is able 

' For bibliography of the literature of soil heat, see Bouyoucos, 
G. J. An Investigation of Soil Temperature and Some of the 
Most Important F'aetors Influencing It. Michigan Agr. Exp. 
Sta., Technical Bui. 17, pp. 194-196. 1913. 
U 289 



290 SOILS: PROPERTIES AND MANAGEMENT 



also to govern the time when his sowing and planting are 
performed in such a way that the soil will be fitted, at 
least as far as heat is concerned, for proper seed germina- 
tion and plant growth. 

207. Relation of heat to germination and growth. — 
In order to sliow the exact relationship of heat to ger- 
mination of seeds and to the growth of plants, the follow- 
ing data from Haberlandt * are given. While these 
tables are not exact, they show clearly the necessity of 
careful control of temperature in the propagation of 
plants : — 

The Relation of Temperature to the Germination of 
Certain Seeds (in Degrees Fahrenheit) 





Minimum 


Optimum 


Maximum 


Corn 


49 


93 


115 


Scarlet bean 


49 


93 


115 


Pumpkins 


52 


93 


115 


Wheat 


41 


84 


108 


Barley 


41 


84 


99 



The Relation of Temperature to the Growth of Certain 
Plants (in Degrees Fahrenheit) 



Wheat . 
Barley . 
Corn 
Peas . . 
Buckwheat 
Melon . 
Pumpkin 



Minimum 



32-40 
32-40 
40-51 
32-40 
32-40 
60-65 
51-60 



Optimum 



77-88 
77-88 
88-98 
77-88 
77-88 
88-98 
98-111 



Maximum 



88-98 
88-98 
98-111 
88-98 
98-111 
111-122 
111-122 



1 Haberlandt, F. Die Oberen und Unteren Temperatur- 
grenze fiir die Keimung der Wichtigeren Landwirthsehaftliclien 
Samereien. Landw. Versuchs. Stat., Band 17, Seite 104-116. 
1874. 



SOIL HEAT 291 

It is noticeable that there are here three groups of 
plants as far as temperature conditions for optimum 
growth are concerned. Wheat represents the crops that 
germinate and grow at a relatively low temperature. 
Corn requires a medium high temperature for proper 
growth, while melons and pumpkins represent crops the 
temperature requirements of which are very high. These 
needs must be supplied for a proper development of such 
plants, and must of course be considered in crop adapta- 
tion as well as in soil management in general. 

208. Chemical and physical changes due to heat. — 
In the soil a certain amount of chemical action is going on, 
no matter what the temperature may be ; but it is with- 
out doubt true that this activity is greatly accelerated by 
an increase in soil heat. This arises from two causes : 
(1) because heat increases the solubility of the soil con- 
stituents ; and (2) because the activity of the soil or- 
ganisms is stimulated to such an extent as to in 
turn influence chemical reaction. The increased pro- 
duction of carbon dioxide is a good example of this re- 
lationship. The warming of the soil in spring and 
summer, therefore, by stimulating the amount of solu- 
tion, increases to a marked extent the constituents avail- 
able for plant growth. 

The effect of temperature is less marked in a direct 
way on the structure of the soil than on its chemical or 
biological nature unless the freezing point is reached. 
At this point, if moisture is present, the soil mass is dis- 
rupted and may become rather granulated if the freezing 
process is often repeated. The practice of fall-plowing 
in order to better the tilth of the soil is really taking advan- 
tage of this natural phenomenon. A change in tem- 
perature also causes the expansion or contraction of the 



292 SOILS: PROPERTIES AND MANAGEMENT 

soil gases and may greatly facilitate their movement. 
This is essentially a physical relationship. It must be 
kept in mind, however, that with heat as with other soil 
factors, no clear-cut and distinct discussion of its effects 
in one direction may be made without considering the 
indirect influences that are continually opening up avenues 
which lead to phases more or less foreign to the one under 
discussion. This serves to emphasize the close correla- 
tion of the various factors and conditions that must be 
dealt with in a study of soils. 

209. Sources of soil heat. — The soil may receive 
heat directly or indirectly from three general sources : 
(1) from the sun, (2) from the stars, and (3) by 
conduction from the heated interior of the earth. 
The two last-named sources are so unimportant as 
to warrant no further discussion, since the amount of 
heat received by the soil therefrom is so small as to be 
negligible. 

The sun, then, either directly or indirectly supplies 
all the heat and energy that make it possible for soils to 
support vegetation. This heat is derived in various ways, 
as follows : — 

(1) By direct radiation of rays, both of light and of 
invisible heat. These rays when absorbed tend to raise 
the temperature of the absorbing medium. This source 
of heat is by far the most important and may be desig- 
nated as the direct method of heat induction. 

(2) A considerable amount of heat may be derived by 
radiation and conduction from the atmosphere surround- 
ing the earth. This heat has of course been originally 
obtained from the sun and is passed on to the soil, the 
length of the waves being somewhat changed in the transi- 
tion. Clouds may sometimes serve as a blanket and shut 



SOIL HEAT 293 

in around the earth heat that would otherwise be entirely 
lost so far as the soil is concerned. 

(3) A certain amount of heat may be brought to the 
soil by precipitation. A warm spring rain, by falling 
on the earth and percolating into its subsoil, may be a 
determining factor in crop growth. Although the 
aggregate amount of heat added in this way is small, 
the opportuneness of its application is of no small 
importance. A warm rain often imparts an impetus 
to plant growth which may be noticeable for many weeks 
afterward. 

(4) A large amount of heat is annually entrapped by 
growing plants. This energy is stored up and may ulti- 
mately be liberated by the decay of the tissue. If such 
oxidation takes place in the soil, as it very largely should 
under good farm management, a certain amount of heat 
is liberated in the soil. How important this is it is 
difficult to say, for such energy is given off so grad- 
ually as to be rendered difficult of measurement. Bac- 
terial activity is very closely allied to the utilization 
of such heat. Except under exceptional conditions, as 
in hotbeds or very heavily manured lands, such heat 
has no appreciable effect in altering the temperature of 
a normal soil. 

210. Factors affecting soil temperature. — The tem- 
perature that the soil of any given locality may attain 
is dependent on a certain group of factors so closely re- 
lated as to make their separate consideration sometimes 
rather difficult. For convenience these factors may be 
listed as follows, the actual temperatures and their 
probable fluctuations under field conditions being re- 
served until the various intrinsic and external factors of 
soil heat have been discussed : — 



294 SOILS: PROPERTIES AND MANAGEMENT 



1 . Specific heat 

2. Absorption 

3. Radiation 

4. Conductivity and convection 

5. Evaporation of moisture 

6. Organic decay 

7. Slope 

8. Heat supply and its effects 

211. Specific heat. — The specific heat of any material 
may be defined as its thermal capacity as compared with 
that of water. It is the ratio of the quantity' of heat 
required to raise the temperature of a given weight of 
the substance one degree Centigrade to the quantity 
needed to change an equal weight of water from 19.5° 
to 20,5° Centigrade. A knowledge of the specific heat 
of soil is important because of the general light it sheds 
on the warming-up of a soil in spring and on its rate of 
cooling in autumn. The data from a number of investi- 
gations, in the order of their priority, is here quoted, 
the calculations being based on dry soil : — 

Weight Specific Heat of Soils 



Pfaundler i 


(1866) 


Liebenberg - 


(1878) 


Fine sand . 


. .1923 


Coarse sand . 


. .1920 


Alluvial soil 


. .2507 


Diluvial loam 


. .2250 


Granite soil 


. .3489 


Fine loam . . 


. .2770 


Humous soil 


. .4143 


Humous loam 


. .3290 


Peat . . . 


. .5069 


Granite soil 


. .3880 



1 Pfaundler, L. Ueber die Warme Capacitiit Verschiedener 
Bodenarten und deren Einfluss auf die Pflanze. Ann. d. 
Physik u. Chcmie, Band 205, Seite 102-135. Leipzig, 1806. 

^ Liebenberg, R. von. See Lang, C. Ueber Warme Capa- 
citat der Bodeneonstituenten. Forsch. a. d. Gebiete d. Agri.- 
Physik, Band I, Siete 118. 1878. 



SOIL HEAT 



295 



Langi (1S78) 
Coarse sand 
Limestone soil 
Humous soil . 
Garden soil 
Peat ..... 



.1980 
.2490 
.2570 
.2670 
.4770 



Patten 2 (1909) 
Norfolk sand . . .1848 
Podunk fine sandy 

loam 1828 

Hagerstown loam .1914 
Leonardtown loam .1944 
Galveston clay . .2097 

Bouyoucos^ (1913) 

Sand 1929 

Gravel 2045 

Clay 2059 

Loam 2154 

Peat 2525 

212. Variations of specific heat. — These figures show 
a considerable amount of variation, part of which is of 
course due (1) to inaccuracies in the designation of the 
materials used, (2) to differences in methods, and (3) 
to differences in technique. Allowing for these probable 
errors, there still seem to be other factors involved. One 
of these might be texture, since, according to the earlier 
investigators, the finer mineral soils seem to possess a 
higher specific heat. The data of Bouyoucos and Patten, 
however, seem to controvert this assumption. An in- 
vestigation more to the point is that of Ulrich.'* In work- 

' Lang, C. Ueber Warme Capacitat der Bodenconstitu- 
enten. Forseh. a. d. Gebiete d. Agri.-Physik, Band I, Seite 
109-147. 1878. 

2 Patten, H. E. Heat Transference in Soils. U. S. D. A., 
Bur. Soils, Bui. 59, p. 34. 1909. 

' Bouyoucos, G. J. An Investigation of Soil Temperature. 
Michigan Agr. Exp. Sta., Tech. Bui. 17, p. 12. 1913. 

* Ulrich. R. Untersuchungen iiber die Warmekapazitiit 
der Bodenkonstituenten. Forseh. a. d. Geb. d. Agri.-Physik, 
Band 17, Seite 1-31. 1894. 



296 SOILS: PROPERTIES AND MANAGEMENT 

ing with various grades of quartz sand he obtained 
practically identical specific heats with the various sepa- 
rates : — 

Specific Heat of Various Grades of Sand as Found by 

Ulrich 



Diameter of Sands in Millimeters 


Specific Heat 


2-1 


.1912 


1-.5 


.1908 


.5-.25 


.1922 


.25-171 


.1919 


.171-.114 


.1919 


.114-.071 


.1904 


.071-.010 


.1890 



It is evident, therefore, not only that texture has no 
very great direct effect on specific heat, but also that 
the controlling factor in the data already quoted is the 
composition of the soil. The predominate minerals 
found in soils possess a specific heat of from .180 to .220.^ 
This rather narrow range would normally be still further 
lessened, since an average soil is a complex of the 
different minerals. Humus, then, possessing a specific 
heat of about .5 must, when added to any soil, in- 
crease markedly its thermal capacity and would un- 
doubtedly be the determining factor in weight specific 
heat of the mixture. 

213. Specific heat based on volume of soil. — Under 
normal coii(litit)iis, however, the soil contains a consider- 
able amount of pore space, and different soils would 

1 Ulrich, R. Untersuchungen iiber die Wiirmekapazitat 
der Bodenkonstitenten. Forsch. a. d. Gob. d. Agri.-Physik, 
Band 17, Seite 1-31. 1894. 



SOIL HEAT 



297 



therefore show diflFerent weights to the cubic foot. A 
specific heat comparison based on weight, therefore, does 
not yield a fair idea of the heat capacities of two soils. 
The multiplication of the weight specific heat by the 
apparent specific gravity of the soil in question will 
obviously yield a volume specific heat, which is a 
much more rational basis for comparison. A quota- 
tion from Ulrich ^ makes clear the value of such a com- 
putation : — 

Specific Heat op Soil Expressed by Weight and by Vol- 
ume OF Soil 



Sand 
Clay 
Humus 



Apparent 
Specific 
Gravity 



1.52 

1.04 

.37 



Specific Heat 
BY Weight 



.1909 
.2243 
.4431 



Specific Heat 
BY Volume 



.2901 
.2333 
.1639 



It is evident that in the first case the specific heat is 
governed by the organic content of the soils in question ; 
the greater the amount of organic material present, the 
higher is the thermal capacity. Such is not the case when 
the specific heat of the soil is calculated on a volume basis. 
In an expression of the thermal capacity on this rational 
basis, namely, that of volume, the apparent specific grav- 
ity, or volume weight, is the dominant factor. The ad- 
dition of humus when this method of expression is em- 
ployed merely serves to lower the volume weight, and 



1 Ulrich, R. Untersuehungen liber die Wiirmekapazitiit der 
Bodenkonstituenten. Forsch. a. d. Geb. d. Agri.-Physik, 
Band 17, Seite 1-31. 1894. 



298 SOILS: PROPEBTIES AND MANAGEMENT 

a reduction of specific heat thereby occurs. Under such 
conditions more heat is necessary to raise the temperature 
of the sand than is the case with the weight expression. 
This is because of its high apparent specific gravity. The 
clay shows very Httle change, as its apparent specific 
gravity is about one ; but the humus exhibits a marked 
falHng-oflF, due to its exceedingly low volume weight. 
The factor that tends to vary the specific heat of dry 
soil under natural conditions, therefore, is the a])parent 
specific gravity, or the volume weight. By deep and 
efficient plowing the farmer may encourage the warm- 
ing of his soil, due to a lowered thermal capacity. By 
increasing its humus content he may attain the 
same result, since the volume w^eight is depressed to 
a markedly greater extent than the specific heat is in- 
creased by the addition of organic matter. In fact, any 
operation on or any addition to the soil that will vary 
its apparent specific gravity will in turn aftect the specific 
heat. 

214. Effect of water on specific heat. — One other 
factor, much more potent than the two already men- 
tioned, is yet to be discussed. This factor is water, so 
universally present in soils and of the greatest importance 
in all natural soil phenomena. As the specific heat of 
water is very high compared with the thermal capacity 
of the soil constituents, any addition of it must naturally 
raise the specific heat of a normal soil. Tiiat moisture, 
not apparent specific gravity nor organic content, is the 
controlling factor is demonstrated from the following 
data, calculated by Ulrich ^ on a volume basis : — 

1 Ulrich, R. Untersuehungen iiber die Warmekapazitjit der 
Bodcnkonstituenten. Forsch. a. d. Geb. d. Agri.-Physik, Band 
17, Seite 27. 1894. 



SOIL HEAT 



299 



The Effect of Soil Moisture on the Volume Specific 
Heat of Soil, the Moisture being Expressed as a Per- 
centage of the Total Water Capacity 



Quartz 
Kaolin 
Humus 



25^ 



a f< w 



.2919 .3300 
.2333 .294.5 
.1647 1.2427 



.3682 
.35.58 
.3207 



^Z^ 

§5^ 



.4063 
.4170 
.3987 



3 "!^ 



.4445 
.4783 
.4767 






.4826 
.5395 
.5548 



IB^ 



.5208 
.6008 
.6328 



5 Wti 



.5589 
.6620 
.7108 






.5972 
.7233 

.7888 






.6353 

.7812 
.8669 



25^ 



.6755 
.8458 
.9449 



It is at once evident, from these data and the accom- 
panying curves (see Fig. 46), that moisture, in its effect 
on the specific heat of an average soil, is so potent as to 





.9 
















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Fig. 46. — Curves showing the effect of moisture on the volume specific 
heat of soils of different texture and humus content. 



300 SOILS: PROPERTIES AND MANAGEMENT 

entirely obscure in most cases the variations due directly to 
such factors as apparent specific gra\ity and humus con- 
tent. Organic matter, because of its high water capacity, 
usually accentuates the dominance of moisture in this 
respect. While a humous soil of low volume weight may 
warm up most easily when dry, its high water content may 
so increase its thermal capacity as to markedly retard 
its temperature changes. This is exemplified b.>' Petit ^ 
and Bouyoucos - in their study of frost penetration in 
peat. This soil was the last to freeze in winter and, 
conversely, the last to thaw in spring. The advantage 
of removing excess water by drainage is of importance 
from this standpoint, as a wet soil is necessarily a colder 
soil in spring than one that is well drained. This at least 
partially accounts for the fact that a sandy soil is usually 
an early one, and is therefore of particular value in truck- 
ing operations. 

215. Absorptive power of soils for heat. — The greater 
proportion of the heat received by the soil is obtained 
by direct radiation from the sun. This radiant heat is 
propelled by free wave action in the ether, the space 
intervening between the sun and the earth being but 
little affected by the transfer. Were the total amount 
of heat received from a vertical sun by any unit surface 
wholly absorbed by a layer of soil twelve inches thick, 
the temperature of the soil would rise thirty degrees 
Fahrenheit an hour. Such is not the case under normal 



^ Petit, A. Untersuchungen liber den Einfluss des Frostes 
auf die Tempera turverhaltnisse der Boden von Verschiedener 
Physikolischer Besehaffenheit. Forsch. a. d. Gob. d. Agri.- 
Physik, Band 10, Seite 285-310. 1893. 

'^ Bouyoucos, G. J. An Investigation of Soil Temperature. 
Micliigan Agr. Exp. Sta., Tech. Bui. 17, p. 214. 1913. 



SOIL HEAT 301 

conditions, however, as the atmosphere continuously 
refracts, reflects, and absorbs a certain amount of this 
radiant energy. ]\Iore important still are certain inher- 
ent qualities of the soil itself which function materially 
in the modification of the amount of heat absorbed. These 
intrinsic factors are color, reflection, texture, and structure. 
216. Effect of color on absorption of heat. (See Fig. 
47.) — In a natural soil it is very difficult to efiect a change 
in soil color without changing the texture, structure, and 
more particularly the constitution, of the particles. In 
order to eliminate these disturbing factors in a study of 
heat, a quartz sand colored with various dyes was used 
by Bouyoucos.^ The following data, taken at Lansing, 
Michigan, on a clear, warm day in August, illustrate 
the general eft'ects of color on absorption : — - 

Effect of Different Colors on Heat Absorption by 
Quartz Sand, August 5, 1.30 p.m. 

Color Temperature 

(Degrees Centigrade) 

Black 37-6 

Blue 36.7 

Red 35.9 

Green 34.7 

Yellow 32.6 

White 31.7 

It is quite evident that the darker the soil, the greater 
is its absorptive power. This is because of differences 
in reflection, a light-colored soil reflecting more of the 
heat rays than one of a darker color. There might be a 
question here as to the difference in radiation arising from 

1 Bouyoueos, G. J. An Investigation of Soil Temperature. 
Michigan Agr. Exp. Sta., Tech. Bui. 17, p. 31. 1913. 



302 SOILS: PROPERTIES AND MANAGEMENT 

color, the white soils radiating more heat than the black 
ones. The following data from Bouyoucos,^ substantiating 
those of Lang,- are a conclusive negative answer to such 
a query : — 

Radiation of Different-colored Sands, White being 
TAKEN AS 1.00 

White 1.000 

Black 991 

Blue 981 

Green 981 

Red 991 

Yellow 989 

The addition of organic matter, provided its decay has 
been of the proper sort, will consequently always raise 
the soil temperature, other factors of course being equal. 
Wollny,^ in experimentation with soils covered with thin 
layers of different-colored material, found marked dif- 
ferences under field conditions. The black soil not only 
exhibited the highest temperature, but also showed a 
greater amount of fluctuation. The minimum tempera- 
tures of the different-colored soils were almost the same. 
The temperature differences of course decreased with 
depth. Some typical data obtained on a clear day, as 
quoted from Wollny's work, are as follows : — 

1 Bouyoucos, G. J. An Investigation of Soil Temperature. 
Michigan Agr. Exp. Sta., Tech. Bui. 17, p. -30. 1913. 

^ Lang, C. tjber Wiirme-absorption und Emission des 
Boden. Forsch. a. d. Gebiete d. Agri.-Physik, Band 1, Soite 
379-407. 1878. 

^ Wollny, E. Untersuehungen liber den Einfluss der Farbe 
des Bodens auf dessen Erwiirmung. Forsch. a. d. Geb. d. 
Agri.-Physik, Band I, Seite 43-69. 1878. Also, Untersueh- 
ungen iiber den Einfluss der Farbe des Bodens auf dessen Erwiir- 
mung. Forsch. a. d. Geb. d. Agri.-Physik, Band IV, Seite 
327-305. 1881. 



SOIL HEAT 



303 



Temperatures of Different-colored Soils at a Depth of 
4 inches, taken June 23, 1876, at Munich (in Degrees 
Centigrade) 



Time 


Air 


Black 


White 


Midnight .... 

2 A.M 

4 

6 

8 

10 

Noon 

2 P.M 

4 

6 

8 

10 


9.6 
10.0 

7.6 
16.0 
19.8 
23.0 
25.4 
25.4 
24.8 
22.6 
19.4 
16.1 


13.8 
12.4 
10.7 
9.6 
10.4 
15.7 
22.1 
26.8 
29.4 
28.8 
27.2 
24.0 


13.8 
12.4 
10.8 
9.6 
10.9 
13.8 
17.6 
21.2 
23.6 
24.0 
23.6 
21.6 

















































I, 




\ 


Nr 


l^C/< 


?/7 












/ 


^ 


7 


f 


>N 






y/7"if" 


It; 










/ 


/ 


/} 


/ 






V 


\J 


-4//B 


to 




^ 


^ 


J 


^^ 




/ 




















^ 


r 




r 
















/} 





























Fig. 47. — Curves showing the temperature variation of different-colored 
soils at a four inch depth compared with air temperature. Munich, 
June 23, 1876. 



304 SOILS: PROPERTIES AND MANAGEMENT 

Besides the quite o})vious effect of tlie dark color on 
the rate of heat absorption, two other points are worthy 
of notice. The first is tlie tendency of the soil tempera- 
ture to lag behind the temperature of the air, and the 
second is the almost equal minimum reached by the two 
soils. The latter point would seem to indicate also that 
color had little differential effect on the heat lost from 
the soil by radiation into the air. 

217. Effects of texture and structure on heat absorp- 
tion. — Ordinarily the texture and the structure of a 
soil, other conditions being equal, have little direct 
influence on rate of absorption. Wollny ^ found with 
dry and moist soil that the coarser the particles, the higher 
is the temperature during warm weather. A loose, open 
structure was always more favorable for high tempera- 
tures than one more finely pulverized. Wollny 's tem- 
perature dift'erences, however, were very small, and it is 
probable that the experimental error, particularly due 
to lack of moisture control, was greater than the observed 
differences. Lender normal conditions the practical effects 
arising from the influence of texture and structure on 
rate of absorption are probably entirely eliminated by 
other factors. The importance of texture and structure, 
as will be shown later, is in the direction of the control 
of soil heat through their influence on soil moisture. 
Moisture in turn is a potent factor in the ultimate soil 
temperature, as it influences specific heat, radiation, and 
evaporation to such an extent. 

218. Radiation of heat by soil. — The principal loss 

1 Wollny, E. Untersuchungen liber den Einfluss der Struk- 
tur des Bodens auf dessen Feuchtigkeits- und Temperatur- 
verhaltnisse. Forsch. a. d. Geb. d. Agri.-Physik, Band V, 
Seite 145-209. 1882. 



SOIL HEAT 



305 



of heat by the soil is through radiation, this radiation 
being controlled by certain factors of which moisture 
content, soil mulches, artificial coverings, shelters, and 
clouds are the most important. Color as a factor in 
radiation has already been eliminated by the work of 
Bouyoucos and Lang. The effects of texture and struc- 
ture have also been investigated by these authors, as 
well as by other physicists. The general results seem 
to indicate that unless a dry soil is dealt with these factors 
may be eliminated from consideration as far as their 
direct practical effect on radiation is concerned. Of 
course, indirectly through their influence on such factors 
as moisture, they are of extreme importance. 

An increase in the moisture of a soil has the general 
effect of heightening the radiation ratio. This, together 
with the effects of evaporation and of increased specific 
heat, accounts for the fact that an undrained soil in spring 
is a cold soil. Bouyoucos ^ found the following relation- 
ships between moist and dry soils : — 

Effect of Moisture on Radiation 



Soil 


Percentage op 
Moisture 


Radiation of 
Moist Soil 


Radiation of 
Dry Soil 


Gravel 

Sand 

Clay 

Loam 

Peat 


4.7 

5.3 

17.2 

25.8 

84.9 


100 
100 
100 
100 
100 


92.4 
93.1 
91.9 
90.9 
86.1 



Mulches, either natural or artificial, tend to check the 
loss of soil heat through their covering effect and their 



1 Bouyoucos, G. J. An Investigation of Soil Temperature. 
Michigan Agr. Exp. Sta., Tech. Bui. 17, p. 34. 1913. 



30G SOILS: PROPERTIES AND MANAGEMENT 

influence on radiation. As a mulch is usually dry, its 
radiant power is lower than that of the moist soil beneath. 
Shelters decrease radiation by checking air movement. 
The vegetation growing on soil also lowers radiation 
through its covering eflPect, although the temperature of 
soils covered with vegetation is usually low in summer 
due to the obstruction of the sun's rays. Clouds, by 
shutting in the heat, tend to check radiation and in many 
cases prevent a frost that would otherwise occur. The 
protecting effect of snow is well illustrated from the fol- 
lowing data, taken from Boussingoult : — 

Effect of Snow on Soil Temperature.^ (Temperature in 
Degrees Centigrade) 



Date and Hour 



Air 



Feb. 11, 5 P.M. . 

Feb. 12, 7 A.M. . 
Feb. 13, 7 A.M. . 
Feb. 13, S.30 p.m. 



+ 2..5 

- 3.0 

- 3.8 

+ 4.5 



On 

Snow 



- 1.5 

- 12.0 

- 8.2 

- 1.0 



Under 
Snow 



0.0 

- 3.5 

- 2.0 
0.0 



One of the important features of soil heat radiation is 
its effect on air temperature. As the radiant energy from 
the sun passes through the atmosphere, very little of the 
heat is appropriated, due to the wave lengths. But, 
as this energy is radiated from the soil, the heat waves 
have become shortened and are readily taken up by the 
atmosphere, particularly if the latter is moist. How- 
ever, as the air is always in motion its heat is not con- 
trolled by the soil radiation of any particular locality. 



1 Warington, R. Lectures on Some of the Physical Proper- 
ties of Soils, p. 159. Oxford. 1900. 



SOIL HEAT 307 

In fact, the soil may be warmed by conduction of heat 
from air to soil. This probably occurs to some extent 
in spring, when the air is growing warmer, due to low 
specific heat and its movement. The changes in air 
temperatures are always more rapid and usually greater 
in range, due to the factors cited above. 

219. Conductivity and convection of heat in soils. — 
While radiation has to do with the transfer of heat by 
ether waves, conductivity is a term used in relation to 
molecular transmission of energy through the body under 
investigation. It may be defined as the amount of heat 
in calories that will pass across a cube of unit edge (1 
centimeter), in unit time (1 second) under a temperature 
gradient of 1 degree Centigrade. Convection refers to 
the transmission of heat by actual apparent and visible 
movements of matter. It is to these two modes of trans- 
fer that we owe the possibility of the soil's warming below 
a surface that receives most of its heat as radiant energy. 
It must be remembered that in studying the soil we are 
dealing with a material made up of mineral and organic 
compounds and always containing, under normal condi- 
tions, a certain quantity of water. Air likewise is always 
present, which, while a poor conductor of heat, may carry 
energy by convection. Besides these varying substances, 
often in loose contact and usually containing air capable 
of considerable movement, there is bound to occur a 
certain amount of transfer conductivity which is the heat 
resistance found at the boundary of two substances in 
contact. The study of heat movement downward through 
a soil is difficult to analyze, since it is almost impossible 
to control the factors concerned while varying any one. 
In a normal soil this heat movement occurs through both 
the agency of conduction and that of convection, depend- 



308 SOILS: PROPERTIES AND MANAGEMENT 



ing on the texture and structure of the soil and the amount 
of moisture present. 

220. Measurement of conductivity. — Ordinarily the 
conductivity of a soil is measured by applying a constant 
source of heat as quickly as possible and measuring the 
change in temperature by means of thermometers set 
in the soil at regular intervals. (See Fig. 48.) The soil in 
question should be homogeneous in composition and of 
uniform compaction, and should contain a definite mois- 
ture content. It should of course be at a temperature 
equilibrium before the heat is applied. Ordinarily radia- 
tion and convection currents are diminished somewhat 
by inclosing the soil in an insulated compartment. The 
study of heat movement downward instead of laterally 
is to be recommended, in order that unnecessary air 
circulation may be avoided to some extent. 







Fig. 48. — Loi 



48. — Longitudinul section of apparatus for the study of heat 
duftivity of soil. (C), water at constant temperature; (0, 
monioter ; (P), copper plates; (F), screw clamp for pressing 
y against source of heat ; (r) , skids for soil box. 



ron- 
ther- 



firnil 



221. Effect of texture on conductivity of heat. — The 

conducti\ity of a soil is affected by a number of factors 



SOIL HEAT 309 

which may or may not lend themselves to modification 
in the field. From the fact that type is of primary im- 
portance in choosing a soil, texture in its relation to con- 
ductivity might be considered first. From the work of 
Wagner ^ and Potts ^ it is clearly established that the 
coarser the texture of a soil, the faster the rate of conduc- 
tion of heat will be, other factors remaining constant. 
Data quoted from the findings of Bouyoucos ^ substantiate 
these results : — 

Conductivity of Various Soils as Measured by the Time 
Required for a Thermometer 7 Inches from the Source 
of Heat to Show a Rise in Temperature 

^ ., Relative Rate of 

Conductivity 

Sand 1.00 

Loam 1.81 

Clay 1.77 

Peat 4.61 

Such results as these are only comparative and qualita- 
tive. The difficulties of quantitative determinations are 
so beset by error that only one investigator has a^ yet 
made any consistent attempt along this line. Patten,"* 
who has prosecuted such an investigation, finds that such 
work may be vitiated by thermometer spacing, size of 
thermometer, error in readings, moisture control, and 

1 Wagner, F. Untersuchungen iiber das Relative Warme- 
leitungsvermogen Verschiedner Bodenarten. Forsch. a. d. 
Geb. d. Agri.-Physik, Band VI, Seite 1-51. 1885. 

"^ Potts, E. Untersuchungen Betreffend die Fortpflan- 
zung der Wiirme in Boden dureh Leitung. Landw. Ver. Stat., 
Band XX, Seite 273-355. 1877. 

' Bouyoucos, G. J. An Investigation of Soil Temperature. 
Michigan Agr. Exp. Sta., Tech. Bui. 17, p. 20. 1913. 

^ Patten, H. E. Heat Transfer in Soils. U. S. D. A., Bur. 
Soils, Bui. 59. 1909. 



310 SOILS: PROPERTIES AND MANAGEMENT 

the necessity- of taking time-temperature (■ur\'es in the 
unsteady state. His results, expressed as metric K (the 
heat conductivity coefficient in C. G. S. units), show the 
same general comparisons as already presented : — 

Heat Conductivity of Different Soils 

K in C.G.S. units 
Soil (See Definition of 



Coarse quartz 
Leonardtown loam 
Podunk fine sandy loam 
Hagerstown loam . 
Galveston clay . 
Muck 



Conductivity) 
.000917 
.000882 
.000792 
.000099 
.000577 
.000349 



222. Effects of humus and structure on conductivity. — 
A disturbing factor always present when soils are used 
in the determination of the effect of texture on conduc- 
tivity, is humus. It is evident, in dry soil at least, that 
an increase in the organic content of a soil means a lower- 
ing in conductivity. Humus, therefore, must be listed 
as » second factor tending to vary the movement of heat 
through soils. A third factor is the structural condition 
of the soil under examination. Wagner ^ has shown in 
this regard that the more compact a soil, the faster is 
the conduction of heat. This is probably due to the more 
intimate contact of the soil grains, and a consequent 
cutting-down of the insulation factors and diminution 
of the transfer resistance. 

223. Influence of moisture on heat conductivity in soil. 
— The greatest single factor to be considered in conduc- 

^ Wagner, F. Untersuchungen iiber das Relative Warrae- 
leitungsvermogen Verschiedner Bodenarten. Forsch. a. d. 
Geb. d. Agri.-Physik, Band VI, Seite 1-51, 1885. 



SOIL HEAT 



311 



tivity study, however, is the moisture content of the soil. 
The following curve for quartz powder, taken from Pat- 
ten's ^ work, illustrates its effect and shows how its influ- 
ence may heavily override the factors already mentioned. 



.C03 




Ml 



S /O /S 

Fig. 49. — Effect of moisture upon the apparent specific volume, heat 
conductivity, and diffusivity of coarse quartz powder. 



• Patten, H. E. Heat Transfer in Soils. U. S. D. A., 
Bur. Soils, Bui. 59, p. 30. 1909. 



312 SOILS: PROPERTIES AND MANAGEMENT 

At first fijlance it appears peculiar that the heat move- 
ment through a soil, the mineral constituents of which 
possess a conductivity coefficient of about .01066, should 
be raised by the addition of a liquid possessing a value of 
K of about .00149, a conductivity about one-seventh of 
the soil minerals. The explanation of this as given by 
Patten is a lowering of the transfer resistance. He has 
calculated that heat will pass from soil to water approxi- 
mately one hundred and fifty times more easily than 
from soil to air. This being true, it is evident that as 
the water is increased in any soil and the air decreased, 
the conductivity coefficient increases. It must be kept 
in mind, however, that as the moisture increases, the 
total amount of heat necessary to raise this soil to a given 
temperature must also be increased. The necessity for 
the maintenance of a medium moisture content in any 
soil becomes apparent, although the conductivity may 
not thereby be at its maximum. The curves in question 
show that not only is there a change of volume weight, 
but also there is a decrease in diffusivity with high water 
percentages — another reason for avoiding excessive 
moisture contents in a field soil. 

As has already been noted, the warming-up of a soil 
becomes less and less rapid as the subsoil is penetrated. 
This is not due to lessened conductivity, but rather to 
a lessened heat supply. Bouyoucos ^ has shown that 
under natural conditions the tendency of heat is to travel 
downward more rapidly than laterally, due to a higher 
moisture in the lower depths of the average field soil. 
The time-temperature curves and the temperature gradi- 



' Bouvoueos, G. J. An Investigation of Soil Temperature. 
Michigan Agr. Exp. Sta., Tech. Bill. 17, p. 25. 1913. 



SOIL HEAT 



313 



ent for quartz powder as drawn by Patten ^ (see Figs. 50 
and 51) illustrate the effect of distance on temperature 
rise, the conductivity coefficient remaining constant. 
Degrees C. 




50 Time /nmirr. 

Fig. 50. — Temperature time curves for quartz powder at various dis- 
tances from the source of heat. 

From this brief discussion of conductivity it may be 
estabhshed that such a movement is of importance to 
plants in carrying heat downward into the soil. While 
it is affected directly by tex- 
ture, structure, and humus 
to a certain extent, moisture 
is the dominant factor. Under 
natural conditions it is neces- 
sary to maintain a medium 
moisture content, although 
the conductivity of heat is 
not then at its maximum. 
However, it must always be 
remembered that convection 
is active under such conditions and may do much in 
facilitating heat distribution. Good tilth and increased 
organic content of any soil, by raising the optimum 



c. 

fln* 


\ 
















60 
4o 


\ 


\ 
















\ 


\ 


















\ 
























— 



/n 



7Cf7? 



D/siance rrom source o//?eat 

Fig. 51. — Temperature gradi- 
ent for air-dry coarse quartz 
powder. 



1 Patten, H. E. Heat Transfer in Soils, U. S. D. A., 
Bur. Soils, Bui. 59, pp. 23-24. 1909. 



314 SOILS: PROPERTIES AND MANAGEMENT 

moisture content for plant fjrowth, will place the soil in 
the best possible condition, consistent with plant devel- 
opment, for good heat movement. 

224. Effect of evaporation of water on soil temperature. 
— There is perhai)s no factor, besides the loss of heat by 
direct radiation, which exerts such an effect on soil tem- 
perature as does evaporation. The fact that water does 
not allow the long rays received by direct radiation to pass 
readily through it accounts for its rapid vaporization. 
This evaporation, caused by an increased molecular 
activity, requires a certain expenditure of heat, result- 
ing in a cooling effect on the water and consequently on 
any material in close contact with it. To evaporate a 
pound of water requires the withdrawal of about 966 
heat units. ^ This is sufficient to lower the temperature 
of a cubic foot of saturated clay soil about 10° Fahrenheit. 
The difference in temperature exhibited by wet and dry- 
bulb thermometers measures the cooling effect of 
evaporation. 

Any condition that increases the rate of evaporation 
lowers the temperature of the surface concerned. The 
amount of water present is undoubtedly the controlling fac- 
tor in this regard. King - found, in his study of a drained 
and an undrained soil in April, that the former maintained 
a temperature ranging from 2.5° to 12.5° Fahrenheit 
higher than the latter. Parks ^ records the same general 

1 An English heat unit is the amount of energy necessary to 
raise one pound of pure water from 32° to 33° F. It is equal to 
about 778 foot-pounds. 

^ King, F. H. Physios of Agriculture, p. 220. Published 
by the author, Madison, Wisconsin. 1910. 

•■' Parks, J. On the Influence of Water on the Temperature 
of Soils. Jour. Rov. Agri. Soc. Eng., Vol. 5, pp. 119-146. 
1845. 



SOIL HEAT 315 

results in England. Wollny ^ finds a wet soil to be the 
cooler in the daytime, the difference being roughly pro- 
portional to the amount of water present. The effect 
of the amount of water on the rate of evaporation is of 
course influenced to a certain extent by texture, struc- 
ture, and humus, since these factors exert such a marked 
influence on water capacity and capillary movement. 

The practical importance of a study of the effect of 
evaporation on soil temperature lies in the fact that evap- 
oration can be controlled to a certain extent under field 
conditions. This is not so true, unfortunately, of radia- 
tion and conduction. Thorough underdrainage is the 
dominant operation in the prevention of cooling by 
evaporation. By this removal of excess water the specific 
heat is lowered, radiation is slightly retarded, and con- 
vection is facilitated. This means a faster warming of 
the soil, tending toward an optimum temperature rela- 
tion as far as the plant is concerned. Optimum moisture 
encourages optimum heat conditions, as well as other 
favorable relations whether chemical, physical, or biologi- 
cal. Drainage, lime, humus, and tillage figure in heat 
control as well as in other phases of soil improvement. 

225. Effect of organic decay on soil temperature. — 
Besifles the effect of organic matter on color and its conse- 
quent influence on the absorption of heat, it may function 
in another direction, namely, in producing heat of fer- 
mentation. How far this liberation of heat under field 



* Wollny, E. Untersuchungen iiber den Einfluss des 
Wassers auf die Boden. Forseh. a. d. Geb. d. Agri.-Physik, 
Band IV, Seite 147-190. 1881. Also, Untersuchungen uber 
den J^influss der Oberfliichlichen Abtrochnung des Boden auf 
dessen Temperatur- und Peuchligkeitsverhaltnisse. Forseh. a. d. 
Geb. d. Agri.-Physik, Band III, Seite 325-348. 1880. 



316 SOILS: PROPERTIES AND MANAGEMENT 

conditions is effective in bringing about any important 
modification of soil temperature it is often difficult to 
decide. In greenhouses and hotbeds perceptible increases 
are obtained by the use of large quantities of fresh manure, 
as high an increase as 75 degrees Centigrade has been 
observed under such conditions. In the field, however, 
where the absorption and radiation of heat are very large, 
where the organic matter makes up only a fraction of the 
soil's components, and where the applications of barnyard 
manure are relatively small compared to the bulk of the 
soil, it is doubtful whether any important increase of 
soil heat actually occurs. Georgeson,^ working in Japan 
with varying quantities of manure, obtained during the 
first twenty days an excess over the check of only 3.4 
degrees Fahrenheit from an application of eighty tons an 
acre. With twenty tons the increase was 1.7 degrees. 
Wagner - obtained similar results, finding an average 
excess of 1 degree Fahrenheit from the use of twenty 
tons of barnyard manure. Bouyoucos ^ has obtained the 
latest data on this subject. Under controlled laboratory 
conditions he found that unless excessive amounts of 
manure were applied no appreciable effects were observed. 
With an application of ten tons the highest rise was one- 
half degree Centigrade ; after one hundred and three 
days the manured soil was only one-fourth degree higher 
than the untreated. Such results show that the heat of 
fermentation has little important practical influence 

1 Georgeson, C. C. Influence of Manure on Soil Tempera- 
ture. Agr. Sci., Vol. I, pp. 25-52. 1887. 

^ Wagner, F. "Dber den Einfluf?s der Dungung mit Organ- 
ischen Substance auf die Bodentemperatur. Forsch. a. d. 
Geb. d. Agri.-Physik, Band V, Seite 373^05. 1882. 

' Bouyoucos, G. J. An Investigation of Soil Temperature. 
Michigan Agr. Exp. Sta., Tech. Bui. 17, pp. 180-190. 1913. 



SOIL HEAT ' 317 

on soil temperature, so far as the total bulk is concerned. 
There are without douht certain localized influences, 
both chemical and biological, but how important they 
may be it is rather difficult to say. From what is known 
at the present time it seems that organic matter exerts 
its greatest temperature effects through the darkening of 
the color and the increase in moisture capacity of the 
soil. 

226. Relation of slope to soil temperature. — The rela- 
tion of exposure to soil heat is the last phase to be con- 
sidered, with the exception of meteorological factors, 
which are external in their relationships rather than intrin- 
sic as have been most of the phases already discussed. 
The slope of a surface varies the amount of heat 
absorbed from the sun, without affecting, of course, the 
absorptive power of the surface in\'olved. The greater 
the inclination of a soil from a right-angle interception 
of the heat rays, the less rapid will be its rise of tempera- 
ture in a given unit of time, the source of heat remaining 
constant. This is because the greater the inclination, 
the greater is the amount of surface a given amount of 
heat must serve. It is evident that a less amount of 
heat will reach each unit of soil surface, and a conse- 
quent slower rise in temperature of the soil so situated 
will result. Under normal conditions, therefore, any 
inclination that will cause a surface to approach a right- 
angle interception of the sun's rays will not only increase 
its rate of temperature rise but at the same time will 
increase its average seasonal temperature. In the North 
Temperate Zone this of course is a southerly inclination. 
The following diagram, illustrating the conditions on the 
42d parallel at noon on June 21, makes clear this rela- 
tionship : — 



318 SOILS: PROPERTIES AND MANAGEMENT 




Fig. 52. — Diagram showing the proportional amount of heat received to 
the unit area by different slopes on June 21, at the 42d parallel north. 

It is seen that in this case a southerly slope of 20° 
receives to a unit area the greatest amount of heat, the 
level soils and the soils having northerly inclination of 
20° differing in the order named. The following table 
shows the proportional amount of heat received by each 
one of these soils per unit area at midday with such an 
inclination of the sun's ravs : — 



Proportional Amount of Heat Received per Unit Area 
BY Different Slopes on June 21, at the 42d Parallel 
North Latitude 

20° Southerly slope = lOG 

Level = 100 

20° Northerly slope = 81 



SOIL HEAT 319 

These figures show not only that the slope itself is impor- 
tant, but also that the direction of the inclination must 
play a part in the selection of land with its probable 
temperature relationships borne in mind. The investi- 
gations of Wollny/ which have since been corroborated 
by King - and others, may be cited at this point as typi- 
cal : — 

Average Temperature at 6 Inches of a Humous Sandy 
Loam from April to October, 1877, Munich, Germany 

Temperature 
in Degrees 
Centigrade 

South 14.46 

Southeast 14.42 

Southwest 14.42 

East 13.99 

West 13.98 

Northwest 13.64 

Northeast 13.56 

North 13.52 

1 Wollny, E. Untersuchungen iiber den Einfluss der 
Exposition auf die Erwarmung des Bodens. Forseh. a. d. 
Geb. d. Agri.-Physik, Band I, Seite 263-294, 1878; Unter- 
suchungen iiber die Feuchtigkeits- und Temperaturverhiilt- 
nisse des Bodens bei Verschiedener Neigung des Terrains gegen 
den Horizont. Forseh. a. d. Geb. d. Agri.-Physik, Band IX, 
Seite 1-70, 1886; Untersuchungen uber die Feuehtigkeits- 
und Temperaturverhaltnisse des Bodens bei Verschiedener 
Neigung des Terrains gegen die Hummelsrichtung und gegen 
den Horizont. Forseh. a. d. Geb. d. Agri.-Physik, Band X, 
Seite 1-54, 1887; Untersuchungen iiber die Temperaturver- 
haltnisse des Bodens bei Verschiedener Neigung des Terrains 
gegen die Hummelsrichtung und gegenden Horizont. Forseh. 
a. d. Geb. d. Agri.-Physik, Band X, Seite 345-364. 1887. 

- King, F. H. Physics of Agriculture, p. 218. Published 
by the author, Madison, Wisconsin. 1910. 



320 SOILS: PROPERTIES AND MANAGEMENT 

Wollny found also that the soil temperature on the 
southward slopes varied according to the time of year. 
P^or example, the southeasterly inclination was highest 
in the early season, the southerly slope during mid-season, 
and the southwesterly slope during the fall. A southeast- 
erly slope is usually preferred by gardeners. Orchardists 
also pay strict attention to aspect, as it often is a factor 
in susceptibility to sun scald and other diseases. 

King, in comparing a red clay with a southerly slope 
of 18° to that on a level on July 21, obtained the follow- 
ing results : — 

Temperature in Degrees Fahrenheit of Red Clay as 

Influenced by Slope 





First Foot 


Second Foot 


Third Foot 


Southerly slope . . . 
Level 


70.3 
67.2 

3.1 


68.1 
65.4 

2.7 


66.4 
63.6 

2.8 



It is apparent immediately that the influence of slope 
is not confined to the surface, but, owing to conduction 
and convection, is felt to a considerable depth. Slope, 
therefore, together with moisture control, becomes a 
dominant factor in the heat relations of a soil. This is 
particularly true with specialized crops, with which the 
early warming of the soil is important. A normally early 
soil may become late because of exposure, or a naturally 
late soil may become earlier due to an inclination south- 
ward. Slope many times is a dominant factor in the 
adaptation of crop to soil. 

227. Heat supply and its effects. — The direct heat 
supply is without doubt the controlling factor in soil 



SOIL HEAT 



321 



temperature, influenced, of course, by the conditions 
already discussed. The effect of this heat supply is re- 
flected in the seasonal, monthly, and daily soil tempera- 
tures at the surface and at varying depths below. The 
following data illustrate the differences that may ordi- 
narily be expected to take place from season, to season on 
an average soil : — 

Average Temperature Readings Taken at Breslau, Ger- 
many. ^ Average of Ten Years, 1901-1910 (in Degrees 
Fahrenheit) 





Air 


1 Inch 
Deep 


8 
Inches 
Deep 


16 
Inches 
Deep 


28 
Inches 
Deep 


40 
Inches 
Deep 


52 
Inches 
Deep 


Winter . . . 


29.4 


28.2 


33.3 


34.9 


37.1 


38.7 


40.6 


Spring . . . 


45.5 


44.9 


45.3 


45.4 


44.5 


43.7 


43.5 


Summer . . . 


63.3 


62.8 


63.4 


63.4 


61.6 


59.3 


57.5 


Autumn . . . 


44.8 


43.7 


48.6 


50.5 


52.1 


52.6 


53.3 



Average Temperature Readings Taken at Lincoln, Ne- 
braska.^ Average of Twelve Years, 1890-1902 (in 



Degrees Fahrenheit) 





Air 


1 Inch 
Deep 


3 
Inches 
Deep 


6 

Inches 
Deep 


12 
Inches 
Deep 


24 
Inches 
Deep 


36 
Inches 
Deep 


Winter . . . 


25.9 


28.8 


28.8 


29.5 


32.2 


36.3 


39.1 


Spring . . . 


49.9 


54.8 


53.6 


51.6 


48.5 


45.7 


44.3 


Summer . . . 


73.8 


83.0 


80.9 


79.1 


73.8 


69.0 


66.2 


Autumn . . . 


53.9 


56.4 


57.6 


57.1 


57.5 


59.3 


60.3 



1 Schulze, B., and Burmester, H. Beoboehtungen iiber 
Temperaturverhaltnisse der Bodenoberflaehe und versehiedener 
Bodentiefen. Internat. Mitt, fiir Bodenkunde, Band II, Heft 
2-3, Seite 133-148. 1912. 

^ Swezey, G. D. Soil Temperatures at Lincoln, Nebraska. 
Nebraska Agr. Exp. Sta., 16th Ann. Rept., pp. 95-102. 1903. 



322 SOILS: PROPERTIES AND MANAGEMENT 

These average readings, taken at different points, are 
supported by the data of other observers.^ It is apparent 
that seasonal variation of soil temperature is considerable, 
even at the lower depths. Tlie surface layers of soil seem 
to vary nearly in accord with the air temperature, and 
therefore exhibit a greater fluctuation than the subsoil. 
In general the surface soil is wanner in spring and sum- 
mer than the lower layers, but cooler in fall and winter. 
The following data taken at Lincoln, Nebraska, may be 
of interest : — 

Average Monthly Temperature Readings ^ taken at Lin- 
coln, Nebraska. Average of Twelve Years. 







1 Inch 
Deep 


3 


6 


9 


12 


24 


36 




Air 


Inches 


Inches 


Inches 


Inches 


Inches 


Inches 






Deep 


Deep 


Deep 


Deep 


Deep 


Deep 


January . . 


25.2 


27.3 


27.8 


28.6 


30.0 


31.2 


35.4 


38.5 


February 


24.2 


27.7 


27.3 


27.8 


28.3 


30.2 


33.5 


35.5 


March . . 


35.8 


38.2 


37.2 


36.6 


35.6 


35.4 


35.4 


35.8 


April . . . 


52.1 


57.5 


56.0 


53.3 


50.6 


49.3 


45.6 


43.8 


May , . . 


61.9 


68.7 


67.5 


65.1 


63.3 


60.7 


56.2 


53.3 


June . . . 


71.0 


78.1 


78.0 


75.7 


73.8 


69.9 


64.6 


61.3 


July . . . 


76.0 


85.1 


83.6 


81.6 


79.3 


75.7 


70.2 


67.4 


August . . 


74.5 


82.9 


81.3 


80.1 


78.5 


75.7 


72.2 


69.8 


September . 


67.6 


73.8 


73.4 


72.0 


70.7 


69.2 


68.7 


67.6 


October . 


55.5 


56.7 


58.4 


57.8 


58.3 


57.8 


60.0 


61.3 


November . 


38.7 


38.7 


40.9 


41.5 


43.3 


44.7 


49.2 


52.2 


December . 


28.3 


31.6 


31.4 


32.0 


33.4 


35.2 


40.1 


43.3 


Average . . 


50.9 


55.5 


55.3 


54.6 


53.8 


52.9 


52.6 


52.5 


Range . . 


51.8 


57.8 


56.3 


53.8 


51.0 


45.5 


38.7 


34.3 



^ Ebermayer, E. Untersuchungen iiber das Verbalten 
Verschiedener Bodenarten gegon Warme. Forseh. a. d. Geb. 
d. Agri-Physik, Band 14, Seite 195-253. 1891. 

^ Swezey, G. D. Soil Temperatures at Lincoln, Nebraska. 
Nebraska Agr. Exp. Sta., 16th Ann. Rept., pp. 95-102. 1903. 



SOIL HEAT 



323 



The upper soil layers vary in accordance with the air 
temperature, the maximum and the minimum occurring 
in the same month. A lagging (see Fig. 53) is apparent 
in the subsoil, due to the slow response of this area to the 
heat penetrating from above. These figures also show 
the surface soil to be warmer in spring and summer, and 
cooler in winter and fall, than the lower depths. The 
surface soil not only never falls as low in temperature as 
the air, but reaches a higher point in summer. This is 
shown in the range of the air and soil temperatures. The 
range for the air is 51.8°, while that for the soil is 57.8°, 
56.3°, 53.8°, 51.0°, 45.5°, 38.7°, and 34.3°, respectively, 
for the depths ranging from 1 inch to 36 inches. While 
this range of soil temperature is greater in the aggregate 
than that of the air, the changes are much slower and 
often extend over a number of days, while the air may vary 
many degrees in an hour. 



SO°f= 














L-..., 












70 










/ 


/•■ 


.-- 












60 








/ 




/■ 




-N 










SO 










f 








\s 








^0 








/ / 














\ 


36' 


30 




/ 


'/■ 
















^C 


3' 


zo 


— . -,. 


"'/ 




















/l/fi 




























</>: 


n n 


-B /Vy 


ta X/: 


« /*f. 


i)Y v/C 


've ^c 


'ir /tc 


/6 .i£ 


°r ocj 


'O /rc 


</ D£ 


c 



Flu. 53. — ^Curves showing the average monthly temperature readings at 
various soil depths. Average of twelve years, Lincoln, Nebraska. 



324 SOILS: PROPERTIES AND MANAGEMENT 

The daily and liourly temjjerature of the air and the 
soil may he fairly constant or rather variable, according 
to conditions. On days of sunshine, however, consis- 
tent changes may be expected. The air temperature rises 
from morning until about two o'clock, when the maxi- 
mum is reached. It then falls rapidly. The soil, how- 
ever, does not reach its maximum temperature until 
later in the afternoon, due to the lagging so apparent in 
soil temperature changes. This lagging is greater in 
the lower layers than at the surface. The following data,^ 
taken on a bright day on jVIay 26 in Germany, illustrate 
the ordinary differences that may be expected in soil 
and air temperatures : — 

Hourly Temperatures taken in Germany on May 26, 1884, 
ON a Loam Soil at 4-Inch Depth (in Degrees F'ahrexheit) 



Hour 



Midnight 

2 A.M. 

4 . . 

6 . . 

8 . . 

10 . . 

Noon . 

2 P.M. 

4 . . 

6 . . 

8 . . 

10 . . 



Air 


Bare Soil 


55.4 


63.5 


54.3 


60.4 


52.7 


58.5 


67.6 


57.0 


76.4 


58.4 


82.0 


63.3 


83.5 


69.8 


85.0 


74.8 


84.2 


77.9 


78.1 


77.7 


68.7 


73.9 


65.1 


69.8 



' Wollnj^ E. Untersucliungou iiber den Einfluss dcr 
Pflanzendecke und der Besehattung auf die Physikolischon 
Eigeiisehaften des Bodens. Forseh. a. d. Geb. d. Agri.-Physik, 
Band 6, Seite 197-256. 1885. 



SOIL HEAT 



325 



B0°/= 










/ 




' — 


-- 


\ 








7n 








} 


/ 




Y 


z' 


\ 


V 




SOJL4-" 




^ 


60 






/ 


1 


/ 


/ 










\ 


/ilR. 








r 


^ 


/ 
















A 


1 < 


, , 


t 


& 


s / 


o /■ 


/ t 


; 4- 


i B 'O T/M£. 



Fig. 54. — -Curves showing the hourly temperatures of bare soil at a 
depth of four inches and of the air above the soil. May 26, Germany. 



The temperature of the soil at the surface may often 
exceed that of the air, and the amount of daily fluctua- 
tion may be greater ; but for the lower depths the tem- 
perature curve flattens out. The subsoil shows but 
little daily, and even monthly, variation, and is affected 
only by seasonal changes. 

228. Control of soil temperature. — The means of 
practical control and modification of soil temperature 
are those commonly in vogue in good soil management. 
The most important factor is, of course, soil moisture. 
Good drainage, proper tilth developed by deep plowing, 
plenty of lime, and sufficient organic matter, favor opti- 
mum moisture conditions. Such moisture regulation 
means a lowered specific heat and good conductivity. 
The use of a soil mulch or an artificial covering not only 
will check evaporation but will markedly retard loss of 
heat by radiation. Any farmer who so controls his soil 



326 SOILS: PROPERTIES AND MANAGEMENT 

moisture that optimum conditions as far as the plant is 
concerned may be obtained, should have no fear of a 
poor utilization of heat. 

The increase of soil humus, of course, may act directly 
in heat control by darkeninji; the color and increasing 
absorption. A soil mulch, being dry, not only checks 
evaporation but lowers radiation while increasing absorp- 
tion. Any methods of handling the land which tend to 
better the physical condition of the soil and increase its 
tilth tend also toward a proper heat control at the same 
time. The whole question may be summarized by say- 
ing that if a farmer adopts a proper system of moisture 
control and at the same time employs methods that tend 
always toward a better physical condition of the soil, 
the problem of control of soil heat will be automatically 
solved. He will then have brought about the best condi- 
tions for heat absorption and will have facilitated conduc- 
tion and convection, while at the same time retarding 
losses by evaporation and radiation. 



CHAPTER XV 

AVAILABILITY OF PLANT NUTRIENTS AS 
DETERMINED BY CHEMICAL ANALYSIS 

Fortunately for mankind, only an exceedingly minute 
proportion of the soil is at any one time soluble in water 
or in the aqueous solutions with which it is in contact. 
It is this great degree of insolubility that gives the soil 
its permanence, for in humid regions, without this property, 
it would be rapidly carried away in the drainage water. 
The portion of the soil that is soluble in the various natural 
solvents with which it comes in contact furnishes mineral- 
food materials for plants. The great mass of soil, which 
is relatively insoluble, is constantly subjected to natural 
processes which very slowly bring its constituents into 
solution. The agents that are concerned in the decom- 
position of rock also act on the soil to bring about its 
further disintegration, and thereby render it more soluble ; 
while added to these are the operations of tillage, which 
contribute to the same end. 

Only the surfaces of the soil particles come into contact 
with the decomposing agents, and hence it is the surface 
matter of the particles that gradually goes into solution. 
The factors that determine how rapidly solution shall 
proceed are: (1) the amount of surface exposed, which, 
as has been seen, varies with the size of the particles ; (2) 
the composition of the particles ; (3) the strength of the 
decomposing and solvent agencies. Were it not for this 

327 



328 SOILS: PROPERTIES AND MANAGEMENT 

process, there woukl soon be no mineral food available 
to plants, as drainage water and the growth of crops take 
up relatively large quantities of these substances each 
year ; but in spite of this loss the soil is able to provide 
at least some plant-food material for each crop, when 
called upon by the plant. 

229. Solubility of the soil in various solvents. — For 
purposes of analyses that are intended to show the amounts 
of mineral plant-food materials in a soil, any one of sev- 
eral difTerent solvents may be used. These solvents differ 
in strength,, and consequently the percentages of the 
various constituents obtained from samples of the same 
soil are different for each solvent. A chemical analysis 
of a soil is a determination of the quantities of the con- 
stituents that have been dissolved in the solvent used. 
Therefore it will readily be seen that the interpretation 
of a chemical analysis must depend largely on the nature 
of the solvent, and, unless the solvent is equivalent in 
its action to some process or processes in nature, the results 
must be entirely arbitrary. 

The methods that have been used for obtaining solu- 
tions of the soil for analysis may be grouped as follows : — 

1. Complete solution of the soil. 

2. Partial solution with strong acids. 

3. Partial solution with weak acids. 

4. Extraction with water. 

230. Complete solution of the soil. — By the use of 
hydrofluoric and sulfuric acids and by fusion with alkalies, 
the entire soil mass may be decomposed and all its inor- 
ganic constituents determined.^ Such an analysis shows 

' Wiley, Harvev W. Principles and Practices of Agri- 
cultural Chemical Analysis, Vol. 1, pp. 398-399. 1906. 



AVAILABILITY OF PLANT NUTBIENTS 



329 



the total quantity of the plant-food materials except 
nitrogen, which is never determined in any of the acid 
solutions but by a separate process.^ A deficiency of 
any particular substance may be discovered in this way, 
but nothing can be learned as to the ability of the plant 
to obtain nutriment from the soil. A rock may show as 
much mineral plant-food material as a rich soil. This 
method of analysis is used only to ascertain the ultimate 
limitations of a soil or its possible deficiency in any essen- 
tial constituent. Results of such analyses are to be found 
in paragraphs 46, 48, 52, 53 of this text. 

231. Partial solution with strong acids. — While sul- 
furic, nitric, and hydrochloric acids have all been used as 
solvents," the one most commonly employed is hydrochloric 
acid of 1.115 specific gravity.^ It has been used to such 
an extent that it may be considered the standard solvent, 
and a statement of a chemical analysis of a soil in this 
country may be considered as based on this solvent unless 
otherwise stated. 



1 Official and Provisional Methods of Analysis. U. S. D. A., 
Bur. Chem., Bui. 107 (revised), p. 19. 1908. 

^ Analyses using concentrated mineral acids on the same soil. 
From Snyder, Harry. Soils. Minnesota Agr. Exp. Sta., Bui. 
41, p. 66. 1895. 



Hydro- 
chloric 



Nitric 



Sulfuric 



Total insoluble percentage 
Potash percentage 
Lime percentage 
Magnesia percentage 
Phosphoric acid percentage 
Sulfuric acid percentage . 



81.20 
0.42 
0.55 
0.40 
0.23 
0.08 



83.45 
0.30 
0.30 
0.32 
0.23 
0.08 



80.45 
0.52 
0.53 
0.52 
0.26 
0.10 



^ Official and Provisional Methods of Analysis. U. S. D. A., 
Bur. Chem., Bui. 107 (revised), pp. 14-18. 1908. 



330 soils: properties and management 

An analysis by this method is supposed to show the 
proportion of plant-food materials in a soil that are in a 
condition to be ultimately used by plants at the time 
when the analysis is made, and the plant-food materials 
that are not dissolved by treatment with hydrochloric 
acid are assumed to be in a condition in which plants 
cannot use them. The difficulty with this assumi)tion is 
that, while treatment with hydrochloric acid of a given 
strength marks a definite point in the solubility of the 
compounds in the soil, it does not bear a uniform rela- 
tion to the natural processes by which these compounds 
become available to the plant. 

In the case of most soils a large proportion is not de- 
composed by treatment with strong hydrochloric acid, 
and the portion that is dissolved may contain a larger or 
a smaller quantity of the agriculturally important ele- 
ments, depending on the character of the soil. Thus if 
calcium is present as a phosphate, a larger proportion 
will be dissolved by the acid than if it is in the form of 
silicate. The form in which potassium occurs also in- 
fluences greatly the amount shown by analysis. 

Snyder ^ has analyzed a number of soils by means of 
digestion with strong hydrochloric acid, and has then 
decomposed the acid-insoluble residue by fusion and 
determined its composition. Veitch - has analyzed soils 
by the hydrochloric acid method and by means of com- 
plete solution. A few examples are given below to show 
how soils may vary in the solubility of their constituents 
in strong hydrochloric acid : — 

1 Snyder, Harry. Soils. Minnesota Agr. Exp. Sta., Bui. 41, 
p. 35. 1895. 

2 Veiteh, F. P. The Chemical Composition of Maryland 
Soils. Maryland Agr. E.xp. Sta., Bui. 70, p. 103. 1901. 



AVAILABILITY OF PLANT NUTRIENTS 



331 



Percentage of Constituents not Soluble in HCl, 
l.llo SP. GR. 





Soil from Minnesota 


Soil fbom Maryland 




Fair 
Haven 


Holden 


Experi- 
ment 
Station 


Colum- 
bia 


Chesa- 
peake 


Hudson 
River 
Shale 


Potash . . . 

Lime . . . ■ 

Magnesia . 

Phosphoric 
anhydride . 

Sulfuric anhy- 
dride 


94 
25 

58 

40 
74 


81 

61 
76 

45 

90 


83 
41 
36 

18 

20 


95 
90 
34 

66 


67 
82 
29 

15 


73 
37 

28 





232. Significance of a strong hydrochloric acid analysis. 
— This method of analysis was originally thought to 
give some indication of both the permanent fertility and 
the immediate manurial needs of a soil ; but for each 
question the accuracy of the deductions is limited by a 
number of conditions that make it impossible invariably 
to predict from an analysis how productive a soil may be 
or what particular manure may be profitably applied. 
It is very apparent that the chemical composition of a 
soil is only one of the many factors affecting its produc- 
tiveness. Unfortunately, not all the factors are under- 
stood, and consequently these unknown ones cannot be 
determined either qualitatively or quantitatively. If 
it ever becomes possible to determine quantitatively all 
the factors entering into soil productiveness in the field 
condition, the problem will be solved. 

233. Relation of texture to solubility. — The ratio of 
sand to clay in a soil, and the distribution of the fer- 
tilizing materials in these constituents, will affect the mini- 



332 SOILS: PROPERTIES AND MANAGEMENT 

mum quantity of any constituent required to produce 
a good crop. Hilgard has shown that the addition of 
four or five volumes of quartz sand to one volume of a 
heavy, but highly productive, black clay soil greatly 
increased the productiveness, while diluting the potash 
content of the mixture to 0.12 per cent and the phosphoric 
acid to 0.03 per cent. It is evident that in this soil the 
plant-food materials were in a condition to be easily 
taken up by the plant when the physical condition of the 
soil was suitable. 

If these small quantities of food elements had been 
distributed in the sand particles as well as in the original 
clay, the result would doubtless have been different. 
Suppose, for example, that fifty per cent of the potash 
and phosphoric acid had been in the sand particles and 
the remainder in the cla>' ; in that case the former, in a 
soil exposing much the less surface to dissolving liquids, 
would be i)roportionately less soluble, and as the minimum 
quantity is approached, as shown by the more dilute soil's 
yielding less than the other, the effect would doubtless 
have been to decrease the production. In some soils, 
particularly those of arid regions, the larger particles 
may carry much of the mineral nutrients, in which case 
it is quite evident that a higher percentage of fertility 
is required than in soils carrying the plant-food material 
largely in the small i)articles. 

234. Nature of the subsoil. — The nature and com- 
position of the subsoil is naturally a factor in determining 
soil productiveness, and must be considered as well as 
the top soil. An impervious subsoil, or a very loose 
sandy one, will confine the i)roductive zone largely to 
the topsoil and hence require a greater proportionate 
amount of fertility in that part of the soil. 



AVAILABILITY OF PLANT NUTRIENTS 333 

235. Calcium carbonate. — A determination of the 
amount of calcium present as a carbonate is important 
as an aid to the interpretation of an analysis of the soil. 
Lime not so combined is generally in the form of a sili- 
cate, or possibly a phosphate. If there is a large quantity 
of calcium carbonate in a soil, the potash, phosphoric 
acid, and nitrogen are likely to be more readily soluble, 
and smaller quantities are sufficient for crop growth, than 
if the calcium is not found in this form. The effect of 
the carbonate of lime on the nitrogen ^ compounds is to 
furnish a base for the acids produced in the formation of 
nitrates, and its presence promotes this process. It 
probably replaces potassium in certain compounds where 
otherwise it would be secured with more difficulty. It 
insures the presence of some phosphates of lime, in which 
form phosphorus is more soluble than when combined 
with iron. The form of the manures to be used on the 
soil will also depend in large measure on the presence 
or the absence of calcium carbonate. For example, 
where calcium carbonate is deficient, steamed bone or 
Thomas slag are likely to be more profitable than super- 
phosphate, and nitrate of soda than sulfate of ammonium. 
Finally, the absence of calcium carbonate indicates the 
need of liming, and if the analyses show a considerable 
quantity of potash and phosphoric acid, but practice 
shows these materials to be somewhat deficient, it is 
probable that liming will be very beneficial, and that 
manures carrying these substances will not be so essential 
as the chemical analysis would indicate. It must be 
stated, howe\er, that there are cases for which these de- 
ductions do not hold, owing to the intervention of other 
factors. 

1 Not determined in the hydrochloric acid extract. 



334 SOILS: PROPERTIES AND MANAGEMENT 

236. Deficiency of ingredients and manurial needs. — 
Many standards have been set for the minimnm quantity 
of each of the important soil constituents that must be 
present in order to insure a producti^'e soil. Experi- 
ence has shown, however, that no definite standards hold 
for all soils. By comparing analyses of soils of known 
productivity with that of a soil under investigation it is 
an easy matter to ascertain whether the soil contains a 
large quantity of each agriculturally important ingredi- 
ent ; but when the quantity of any constituent is low, 
it becomes a difficult matter to tell how this will affect 
the agricultural value of the soil. Some soils will be 
productive with 0.05 per cent of phosphoric anhydride, 
while others are unproductive when all the plant nutrients 
are present in ample quantity. 

The fact that the degree of productiveness of a soil 
cannot always be gauged by its analysis gives rise to a 
similar imcertainty with regard to its manurial needs. 
A soil may contain potassium in very large quantities, 
sufficient to produce crops for hundreds of years, as indi- 
cated by a strong hydrochloric acid analysis, and yet a 
potassium salt may be used with profit. On the other 
hand, it is evident that as the content of any constituent 
becomes less, the probable need for its application be- 
comes greater, and a knowledge of the composition of 
the soil thus suggests a j)ractice without assuring its 
success. An analysis of the hydrochloric acid extract, 
therefore, cannot be taken as an infallible guide to the 
fertilizer needs of a soil, and of itself should not be relied 
upon ; but in connection with other knowledge, particu- 
larly that derived from fertilizer tests, it may be useful. 

237. Partial solution with weak acids. — The difficulty 
in judging of the properties of a soil from the results of 



AVAILABILITY OF PLANT NUTRIENTS 335 

a strong hydrochloric acid analysis has led to the use of 
weak acids for obtaining the solution. These weak acids 
dissolve much less of the soil constituents than do the 
strong acids, and the portion so dissolved is supposed to 
represent more nearly the amount that the plant can make 
use of. Both dilute organic acids and dilute mineral 
acids have been used. Among the former are citric, 
acetic, oxalic, and tartaric acids. The assumption on 
which the use of the organic acids is based is that they 
correspond to the solvent agents in the soil combined with 
the solvent action that the plant is supposed to possess, 
and thus dissolve from the soil the quantities of nutrients 
that the plant could take up if it came in contact with 
all the soil particles to a depth represented by the sample 
analyzed. 

238. Advantages in the use of dilute acids. — The ac- 
tion of each of these dilute acids on the same soil does 
not give equal quantities of the various constituents in 
solution. The dilute acids naturally dissolve a much 
smaller amount of material from the soil than does strong 
hydrochloric acid. The dilute acids permit the detection 
of smaller quantities of easily soluble phosphoric acid and 
potash than does the latter, larger quantities of soil being 
used. For example, a chemical analysis of the strong 
hydrochloric acid solution is very likely not to show any 
increase in the phosphorus or potassium in a soil that may 
have been abundantly manured with these fertilizers 
and its productiveness greatly increased thereby. This 
is because the amount of plant-food material added is so 
small in comparison with the w^eight of the area of soil 
nine inches deep over which it is spread that the increase 
in percentage may well come within the limits of analytical 
error. An acre of soil nine inches deep weighs about 



336 SOILS: PROPERTIES AND MANAGEMENT 

2,500,000 pounds. If to this there is added a dressing 
of 2500 i)ounds of phosphoric acid fertihzer containing 
400 pounds of phosphoric acid, it would increase the per- 
centage of that constituent in the soil only 0.016 per cent 
— a difference that could not be detected by the analysis 
of the hydrochloric acid solution. 

239. The one-per-cent citric acid method. — This 
method was proposed by Dyer ^ and was shown by him 
to give results with Rothamsted soils that permitted of 
an accurate estimation of their relative productivity. 
Dyer adopted the one-per-cent strength as the result of 
an investigation in which he determined the acidity of 
the juices in the roots of over one hundred species or 
varieties of plants representing twenty difl'erent natural 
orders. The average acidity of the juices of the twenty 
orders, calculated to crystallized citric acid, was 0.91 
per cent, which led Dyer to adopt a strength of 1 per cent. 
It must be said, however, that the different varieties 
varied greatly in this respect, some having ten times as 
much acidity as others. The implication is that plants pro- 
duce a solvent action on a soil in proportion to the acidity 
of their juices, but an examination of Dyer's figures does 
not show that the size of the croj) ordinarily produced by 
the plants tested would in many cases correspond to the 
acidity of these juices. Thus, of the Crucifera^ the horse- 
radish has several times the acidity of the Swedish turnip 
or of the field cabbage, although the crop produced by the 
former is much less than that of the latter. 

240. Usefulness of the citric acid method. — As shown 
by Dyer, the use of a one-per-cent solution of citric 

' Dyer, Bernard. On the Analytical Determination of Prob- 
ably Available "Mineral" Plant Food in Soils. Jour. Chem. 
Soc, Vol. LXV, pp. 115-167. 1894. 



AVAILABILITY OF PLANT NUTRIENTS 337 

acid is well adapted to show the amount of easily 
soluble phosphoric acid and potash in certain soils, but 
for other soils it has failed to give satisfaction in 
the hands of a number of analysts. It is doubtless 
best suited to soils rich in calcium and low in iron and 
aluminium. 

The reason urged by Dyer for the superiority of the 
citric acid method o^'e^ the hydrochloric acid extraction 
is that soils, shown by experience to need phosphoric 
manures, yielded a relati\'ely much greater quantity of 
phosphorus to citric acid than to hydrochloric acid when 
compared with soils not needing this element. 

The application of both the hydrochloric and citric acid 
methods to a soil, when used to supplement each other, 
may add greath' to a knowledge of the potential and 
present productiveness of the soil. 

According to Dyer,^ for cereals and for most other 
crops there should be present in a soil at least .01 per cent 
of phosphoric acid, soluble in one-per-cent citric acid. 
A soil containing less than this quantity is deficient in 
phosphoric acid, unless this acid exists largely in the form 
of ferric or aluminium phosphate, which is not readily 
soluble in citric acid but is fairly available to the plant. 
Sod land contains organic compounds of phosphorus that 
are readily available to the plant ; hence such soil, to 
indicate sufficiency, should show by analysis more than 
0.01 per cent of phosphoric acid. The quantity of potash 
soluble in the same solvent should also be not less than 
0.01 per cent in arable land. 

1 Dyer, Bernard. A Chemical Study of the Phosphoric 
Acid and Potash Contents of the Wheat Soils of Broadbalk 
Field, Rothamsted. Philosoph. Trans. Royal Soc. London, 
Series B, Vol. 194, pp. 235-290. 1901. 
z 



338 SOILS: PROPERTIES AND MANAGEMENT 

241. Dilute mineral acids. — Of the mineral acids 
in a diluted form used for extracting soils, tho.se that 
have recei\ed the most attention are one-fifth normal 
nitric ^ or hydrochloric acid and one two-hundredth 
normal hydrochloric acid.^ The methods employing 
these solvents are admittedly empirical. There* is no 
natural relation between these solvents and the processes 
by which the plant obtains its nutriment from the soil. 

The solvent that has received the most attention is 
one-fifth normal nitric acid. In ease of manipulation 
this is preferable to the one-per-cent citric acid, wliich is 
rather tedious to work with. It has been used nearly 
as extensively in this country as the latter has in Great 
Britain. Its use has been confined largely to the deter- 
mination of the readily available phosphorus and potas- 
sium in the soil, as has the citric acid method. It is 
obvious that some minerals are more readily soluble than 
are others, and for that reason the method will distinguish 
between phosphorus and potassium in different forms. 
The calcium phosphates are supposed to be entirely soluble 
in this solvent. According to Fraps ^ it dissolves iron 
and aluminium phosphates to only a slight extent, thus 
distinguishing between these forms of phosi)horus. Fraps 
finds also that no potassium is remo\ed from orthoclase 
and microcline, that less than ten per cent is dissolved 



1 Official and Provisional Methods of Analysis. U. S. D. A., 
Bur. Chem., Bui. 107 (revised), p. 18. 1908. 

2 Wiley, H. W. Principles and Practice of Agricultural 
Analysis, pp. 394-396. Easton, Pennsylvania. 1906. 

' Fraps, G. S. Active Phosphoric Acid and Its Relation 
to the Needs of the Soil for Phosphoric Acid in Pot Experi- 
ments. Texas Agr. Exp. Sta., Bui. 12(i, pp. 7-72. 1909. 
Also, The Active Potash of the Soil and Its Relation to Pot 
Experiments. Texas Agr. E.xp. Sta., Bui. 145, pp. 5-39. 1912. 



AVAILABILITY OF PLANT NUTRIENTS 339 

from glauconite and biotite, and that from fifteen to sixty 
per cent is dissolved from muscovite, neplielite, leucite, 
apophyllite and phillipsite. 

Tliere are several factors, however, that make the use 
of one-fifth normal nitric acid an uncertain guide to the 
available phosphorus and potassium in the soil. When 
a soil is treated with the acid some of it is neutralized by 
the reactions that result and thus its strength is lessened. 
This may have no relation to the quantities of phosphorus 
or potassium dissolved. Some analysts correct for the 
neutralization and some do not. Again, as with strong 
hydrochloric acid, the degree of solubility of the soil con- 
stituents in the nitric acid may not correspond with the 
ability of the plant to obtain these substances. With 
this, as with the other methods discussed, the objection 
holds that the result cannot be taken as an infallible guide 
to the producti\'eness of a soil, or to its fertilizer needs ; 
but each of the methods affords some information in 
regard to a soil, and is thus of value. 

242. Extraction with an aqueous solution of carbon 
dioxide. — As carbon dioxide is a universal constituent 
of the water of the soil, and without doubt a potent factor 
in the decomposition of the mineral matter, it has been 
proposed to use a solution of carbon dioxide as a solvent 
in soil analysis. The amounts of soil constituents taken 
up by this sohent are much less than are taken up by 
any of the others heretofore mentioned, but all mineral 
substances used by plants are soluble in it to some extent. 
The amount of phosphorus is so small as to make its 
detection by the gravimetric method difficult. Like 
other methods employing very weak solvents, this method 
is open to the objection that the extraction fails to remove 
a considerable portion of the dissolved matter that is 



340 SOILS: PROPERTIES AND MANAGEMENT 

retained by adsorption, and as this varies with soils of 
different texture a fair comparison of such soils is impos- 
sible. 

243. Extraction with pure water. — When soil is di- 
gested with distilled water, all the mineral substances 
used by plants are dissolved from it, but in very small 
quantities. It has been proposed to use this extract for 
soil analysis on the ground that it involves no artificial 
solvent the presence or amount of which in the soil is 
doubtful, but shows those substances that are undoubtedly 
in a condition to be used by plants. By determining the 
water content of the soil and using a known quantity of 
water for the extraction, the percentage of the various 
constituents in the soil water or in the dry soil may be 
calculated. 

The substances dissolved from the soil by extraction 
with distilled water are probably only those contained 
in the soil-water solution, including a part of the solutes 
held by adsorption. The aqueous extract does not con- 
tain the entire quantity of the nutritive salts in solution 
in the soil water, and hence is not a measure of the 
fertility held in that form. An undetermined quantity 
of nutrients is retained in the water, in the very small 
spaces and on the surface of the soil particles. It is, 
however, a fair comparative measure of the content of 
available nutrients. 

244. Influence of absorption. — The quantity of ex- 
tracted material depends on the absorptive properties of 
the soil and on the amount of water used in the extrac- 
tion, or on the number of extractions. Analyses of the 
aqueous extract of a clay and of a sandy soil on the Cornell 
University farm serve to illustrate the greater retenti^■e 
power of the former for nitrates. Sodium nitrate was 



AVAILABILITY OF PLANT NUTRIENTS 



341 



applied to a clay soil and to a sandy loam soil at the rate 
of ()4() pounds to the acre. Analyses of aqueous extracts 
some ninety daAs later showed the following : — 



Kind op Soil 


Fertilizer 


Nitrates in Soil 
(Parts per million) 


Clay 

Clay 

Sandy loam 

Sandy loam 


Sodium nitrate 
No fertilizer 
Sodium nitrate 
No fertilizer 


7.8 

1.8 

. 150.0 

29.7 



There was apparently a much greater retention of 
nitrate by the clay soil, as shown by a comparison of the 
fertilized and the unfertilized plats on both soils. 

Schulze ^ extracted a rich soil by slowly leaching 1000 
grams with pure water, so that one liter passed through 
in twenty-four hours. The extract for each twenty-four 
hours was analyzed every day for a period of six days. 
The total amounts dissolved during each period were as 
follows : — 



Successive Extractions 


Total Matter 
Dissolved 

(Grams) 


Volatile 
(Grams) 


Inorganic 
(Grams) 


First 


0.535 


0.340 


0.195 


Second 


0.120 


0.057 


0.063 


Third 


0.261 


0.101 


0.160 


Fourth 


0.20.3 


0.083 


0.120 


Fifth 


0.260 


0.082 


0.178 


Sixth 


0.200 


0.077 


0.123 



1 Schulze, F. Ueber den Phosphorsaure-Gehalt des Wasser- 
Auszugs der Ackererde. Landw. Vers. Stat., Band 6, Seite 
409^12. 1864. 



342 SOILS: PROPERTIES AND MANAGEMENT 

It will be noticed that tlie dissolved matter, both or- 
ganic and inorganic, fell oft' markedly after the first ex- 
traction, which was larger because of the matter in solu- 
tion in the soil water. Later extractions were doubtless 
supplied largely from the substances held by adsorption, 
which gradually diffuse into the water extract as the 
tendency to maintain equilibrium of the solution overcomes 
the adsorptive action. \Yith the removal of the adsorbed 
substances, the equilibrium between the soil particles 
and the surroimding solution is disturbed, sohent action 
is increased, and more material gradually passes from the 
soil into the solution. In this way the uniform and con- 
tinuous body of extractives is maintained. 

245. Other factors influencing extraction. — For pm*- 
poses of soil analysis, the quantity of water used for extrac- 
tion must be placed at some arbitrary figure, and this 
is open to the objection that it does not represent accu- 
rately the soil-water solution. Analyses of soils of different 
types are not comparable, and the water extract cannot 
be considered as measuring the concentration, or even 
the composition, of the solution existing between the 
root hair and the soil particles. However, for studying 
some of the changes which go on in the soil and which are 
detectable in the soil-water solution, the practice may be 
followed to advantage. 

246. The soil solution in situ. — It has already been 
pointed out that the interstitial spaces of any arable soil 
contain more or less water all the time ; that there is a 
constant tendency for this water to assume the capillary 
condition owing to the gravitational movement of free 
water ; and that the normal e\aporation of moisture from 
the soil tends to reduce the capillary film to the condition 
of hygroscopic water (par. 132). As the movement 



AVAILABILITY OF PLANT NUTRIENTS 343 

of free water is comparatively rapid and that of capil- 
lary water relatively slow, the soil moisture supply is 
usually somewhere between the point of lento-capillarit\' 
and free water. In this condition each particle or aggre- 
gation of particles is enveloped in a thin moisture film, 
and this film water is constantly in motion although the 
movement is rather slow. 

Soils are more or less soluble in pure water ; and in soil 
water, charged as it always is with carbon dioxide, they 
are still more readily soluble. Consequently the moisture 
films constantly tend to approach a state of equilibrium 
with respect to the water-soluble matter in the soil parti- 
cles. If plants are entirely dependent for their mineral 
nutrients on the supply in the soil-water solution, the 
strength of this solution becomes an important matter. 
The supply of mineral nutrients for higher plants will be 
discussed later (par. 339). Even if the plant itself 
has no influence on the supply of mineral nutrients that go 
into solution, the quantity of food that it finds in the 
soil solution already prepared for its use must constitute 
an important factor in its growth. 

Unfortunately there is no adequate method of ascer- 
taining the strength of the solution. Attempts have 
been made to remove this solution from the soil, but it 
is altogether unlikely that the analyses of the liquid 
obtained represent the composition of the soil solution, 
because of the very small quantity of the liquid available 
for analysis and also because of the uncertainty that the 
sample obtained was representative of the soil solution. 

247. Devices for obtaining a soil solution. — An at- 
tempt by Briggs and McLane ^ to sample the soil solution 

1 Briggs, Lyman J., and McLane, John W. The JNIoisture 
Equivalent of Soils. U. S. D. A., Bur. Soils, Bui. 45, pp. 6-8. 1907. 



344 SOILS: PROPERTIES AND MANAGEMENT 

involved the use of centrifuji;al motion, which developed 
a force of two or three thousand times that of gravita- 
tion. When the soil contained a rather large quantity 
of capillary water, a small amount of it could be removed 
in this way. 

Another device, by Briggs and AlcCall,^ consists of a 
close-grained, unglazed, porcelain tube, closed at one end 
and provided at the other with a tubulure, by which it 
can be connected with an exhausted receiver. This 
tube is moistened and buried in the soil. If the moisture 
content of the soil is sufficient to reduce the pressure of 
the capillary water surface in the soil to less than the dif- 
ference between the pressure inside and outside of the 
tube, there will be a movement of water inward. This 
water may be collected and analyzed. 

IVIore recently Van Suchtelen has used another method 
to obtain the soil solution.- He replaces the soil water 
by means of paraffin in a liquid state, at the same time 
subjecting the soil to suction on a filter. The displaced 
welter is considered to represent the soil solution. 

248. Composition and concentration of the soil solu- 
tion. — It has generally been held that because some soils 
are more producti\e than others, and because fertilizers 
containing soluble salts frequently increase the yields of 
crops, the soil solution in the lietter-yielding soils is more 
concentrated, at least as regards plant nutrients, than is 
that in the poorer soils. The argument is, of course, 



I Briggs, L. J., and McCall, A. G. An Artificial Root for 
Inducing Capillary Movement of Soil Moisture. Science, 
N. S., Vol. 20, pp.' 560-569. 1904. 

^ Van Suchtelen, F. H. H. Methode znr Gewinnung der 
Natiirlichen Bodenlosung. Jour. f. Landw., Band 00, Seito 
309-370. 1912. 



AVAILABILITY OF PLANT NUTRIENTS 345 

based on the assumption that, other things being equal, 
plant growth is a function of the concentration of the 
plant nutrients in the soil solution. According to this 
conception, increased or decreased soil fertility is reflected 
in the composition and concentration of the soil solution, 
and this in turn in crop yields. The soil solution is there- 
fore a variable quantity, and, to some extent at least, within 
the control of man. An elaborate explanation for the 
responsiveness of the soil solution has been worked out 
by Van Bemmelen and his school. 

249. Variability in composition and concentration of 
the soil solution. — The process of rock weathering has, 
according to Van Bemmelen,^ Biltz,- and others, resulted 
in deep-seated chemical changes in some of the mineral 
constituents of the soil, whereby there are formed com- 
plex colloidal silicates which, in the form of gels, cover 
the surfaces of the soil particles. These colloidal com- 
plexes may contain iron, aluminium, calcium, magnesium, 
potassium, phosphorus, and other substances, which are 
absorbed from the diflPerent electrolytes as ions or as 
salts and depend in quantity on the concentration of the 
solution from which they are absorbed. They therefore 
act like solid solutions, whose composition changes 
with every change in the concentration of the liquid solu- 
tion that comes in contact with them. This relation of 
the colloidal complexes to the soil water with which they 
come in contact is essentially different from that of the 

1 Van Bemmelen, J. IM. Beitrage zur Kenntniss der 
Verwitterungsprodukte der Silikate in Ton, Vulkanischen, und 
Laterit-Boden. Zeit. f. Anorganische Chemie, Band 42, 
Seite 265-324. 1904. 

- Biltz, W. Ueber die Gegenseitige Beeinflussung Col- 
loidal Geloster Stoffe. Ber. deutsch. chem. Gesell., Band 
37, Seite 1095-1116. 1904. 



346 SOILS: PROPERTIES AND MANAGEMENT 

pure minerals, as they are not true chemical combina- 
tions. The organic matter in the soil adds another class 
of colloidal matter ; so that, in the opinion of Van Bem- 
melen,^ the colloidal silicates and the colloidal humus form, 
in various proportions, a mass of colloidal complexes that 
control the composition of the soil solution. The col- 
loidal condition of this material is readily flecomposable 
under variations in temperature and concentration of 
solutions, and would doubtless be in a state of constant 
transition in the soil. 

This conception of the soil surface would account for 
changes in the concentration of the soil solution due to 
the application of soluble fertilizers, and would also 
explain the continued effect of such fertilizers on the 
theory that they are absorbed by the colloidal complexes 
and redissolved as the soil solution tends to become more 
dilute. 

A somewhat different view has been taken by Whitney 
and Cameron, who hold that the composition and con- 
centration of the solution in all soils is practically the 
same. Their conception, according to a recent paper by 
Cameron,- appears to differ from that of Van Bemmelen 
in assuming that the soil water is in contact with the soil 
particles for such a short time that the quantity of matter 
that goes into solution is too slight to bear any relation 
to the total quantity of soluble matter in the soil. The 
soil solution does not come into equilibrium with the 
soil mass, nor even approximate such a condition. The 

1 Van Bemmelen, J. M. Die Zusaramensetzung der Aeker- 
erde. Landw. Vers. Stat., Band 37, Seite 347-373. 1890. 

^ Cameron. F. K. Concentration of the Soil Solution. 
Original Communications, Eighth International Congress of 
Applied Chem., Vol. 15, pp. 43-48. 1912. 



AVAILABILITY OF PLANT NUTRIENTS 347 

solution being similar in all soils, it follows that the rela- 
tive productiveness of different soils bears no relation to 
the supply of soluble nutrients, but must be due to other 
factors. Hence soluble fertilizers increase plant growth, 
not by supplying a greater quantity of plant nutrients, 
but through other effects on the soil — as, for instance, 
their favorable influence on tilth, or through the de- 
struction of toxic matter. 

250. Discussion of the theories regarding soil solu- 
tions. — The difficulty in securing a true sample of the 
soil solution as it exists in situ complicates any attempt 
to ascertain how these theories comport with the actual 
condition of the soil solution. A number of attempts 
have been made to throw light on this subject, but none 
of the data obtained is of a nature to definitely prove the 
correctness of either theory. The evidence, so far as it 
goes, indicates that the water extract of soils differs in 
concentration in different soils, and is increased, under 
some conditions, by large and continued applications 
of soluble fertilizers. There can be no doubt, more- 
over, that plant growth in properly balanced nutrient 
solutions increases with the concentration of the solu- 
tion up to several thousand parts to the million, as has 
been demonstrated by many experiments. 

One rather convincing experiment may be quoted. 
Hall, Brenchley, and Underwood ^ analyzed the water 
extract from certain plats on the Rothamsted Experi- 
ment Station farm, the fertilizer treatment and the 
yields of which had been recorded for a long term of years. 

1 Hall, A. D., Brenchley, W. E., and Underwood, T. M. 
The Soil Solution and the Mineral Constituents of the Soil. 
Philosoph. Trans. Royal Soc. London, Series B, Vol. 204, pp. 
179-200. 1913. 



348 SOILS: PROPERTIES AND MANAGEMENT 

Complete analyses of the soil from the several plats were 
also made : — 

Yields of Crops, and Composition op Soil and Water 
Extract of Soil, on Rothamsted Experiment Station 
r"'ARM 



Unmanured . 
N + P,05 . . . 
N + K2O . . . 
Complete fertilizer 
Farm manure . . 



Yield 

TO THE 

Acre 
(.Pounds) 



1,276 
3,972 

2,985 
5,087 
6,184 



Complete Analysis 



P2O6 
(percentage) 



0.099 
0.173 
0.102 
0.182 
0.176 



K2O 

(percentage) 



0.183 
0.248 
0.257 
0.326 
0.167 



Water Extract 



P2OS 
(p. p. m.) 



0.525 

3.900 
0.808 
4.025 
4.463 



K2O 

(p. p. m.) 



3.40 

3.88 
30.33 
24.03 
26.45 



A similarly treated set of plats, which had been planted 
to another crop and analyzed as were these, gave similar 
results. It is a very striking example of the effect of 
long-continued treatment of the soil with a certain fertilizer 
on the composition of the water extract. The subject, 
however, must be investigated further, as it is of funda- 
mental importance to a knowledge of the properties of 
soils. 



CHAPTER XVI 
THE ABSORPTIVE PROPERTIES OF SOILS 

If the brown water extract from manure is filtered 
through a clay soil not containing soluble alkalies, the 
filtrate will be nearly colorless. Many solutions of dye- 
stuffs are affected in the same way. Solutions of alkali 
or alkaline earth salts are more or less modified by this 
operation, the bases being retained by the soil to a greater 
extent than are the acids. Thus, when a solution of 
the nitrate, sulfate, or chloride of any one of these bases 
is filtered through the soil, a part of the base is absorbed 
by the soil, while most of the acid comes through in the 
filtrate. If these bases are in the form of phosphates 
or silicates, not only the base is absorbed, but the acid 
as well. 

251. Substitution of bases. — Associated with the 
absorption of the base from solution, there is liberation 
of some other base from the soil, which combines with 
the acid in the solution and appears in the filtrate as a 
salt of that acid. 

\Yhen absorption takes place from solution, the base 
is never entirely removed, no matter how dilute the solu- 
tion may be. A dilute solution of potassium chloride 
filtered through a soil will produce a filtrate containing 
some calcium, magnesium, or sodium chloride, or all 
these salts, and some potassium chloride. The more 
dilute the solution, the larger will be the proportion re- 

349 



350 SOILS: PROPERTIES AND MANAGEMENT 

tallied, but the less the total quantity absorbed. Peters ^ 
treated 100 grams of soil with 250 cubic centimeters of a 
solution of potassium salts, and found that the potassium 
of different salts was retained in different proportions, 
and that the stronger solutions lost relatively less than 
the weaker, while more potassium was removed from the 
stronger solutions. 



Strength op Solution 


^B Normal 


iV Normal 


Grams K2O absorbed 


Grams K2O absorbed 


KCl 

K2SO4 

K2CO4 


0.3124 

0.3302 
0.5747 


0.1990 

0.2098 
0.3134 



The same bases are not always absorbed in the same 
proportion by different soils ; one soil may have a greater 
absorptive power for potassium, while another may re- 
tain relatively more ammonia. They seem to be inter- 
changeable, as any absorbed base may be released by 
another in solution. The absorptive power of a soil for 
certain bases is reflected in the composition of the drainage 
water from the soil. The composition of the drainage 
water varies with different soils, and a soluble fertilizer 
applied to one soil will have a different effect on the com- 
position of the drainage water than if applied to a different 
soil. This is well illustrated from lysimeter experiments 
by Gerlach - at Bromberg. Several soils were used, 

1 Peters, E. Ueber die Absorption von Kali dureh Acker- 
erde. Landw. Vers. Stat., Band 2, Seite 113-151. 1860. 

^ Gerlach, Dr. Uber die dureh siekerwasser dem Boden 
Entzogenen Menge Wasser iind Nahrstoffe. 111. Landw. Zei- 
tung, 30 Jahrgange, Heft 95, Seite 871-881. 1910. 



THE ABSORPTIVE PROPERTIES OF SOILS 351 

one of each being fertilized and one unfertilized. The 
lysimeters were 1.2 meters deep and contained 4 cubic 
meters of soil. The drainage water was caught and 
analyzed for four years. The first year there was no 
crop, the second year potatoes were grown, the third 
oats, and the fourth rye. The following results were 
shown : — 

Average Composition of Drainage Water in Parts per 

AIlLLION 



Soil 


Treatment 


Total 

Nitrogen 


Nitric 
Nitrogen 


Organic 

Nitrogen 


K2O 


CaO 


Moor soil . 

Loamy sand 
low in humus 

Sandy loam 
high in humus 


j Fertilized 
1 Untreated 

f Fertilized 
\ Untreated 

1 Fertilized 
\ Untreated 


32.7 
65.0 

25.5 
20.9 

67.8 
69.5 


30.0 
60.3 

25.1 
20.4 

64.6 
66.1 


2.7 
4.7 

0.4 
0.5 

3.1 
3.4 


32.2 
26.2 

25.1 

8.5 

70.2 

47.4 


405 
507 

92 
90 

399 
414 



Absorption will not proceed to an unlimited extent. 
A soil will cease to absorb any particular substance after 
a certain quantity has been taken up. This quantity 
will vary with every soil. Clay and loam soils have 
greater absorptive power than sandy soils. This differ- 
ence, both as to amount and as to rate of absorption, is 
well shown by the following curves adapted from Schreiner 
and Failver.^ 



1 Schreiner, O., and Failyer, G. H. The Absorption of 

Phosphates and Potassium by Soils. U. S. D. A., Bur. Soils, 

Bui. 32. 1906. See also Cameron, F. K., and Bell, J. M. 
The Mineral Constituents of the Soil Solution. U. S. D. A., 

Bur. Soils, Bui. 30, pp. 42-66. 1905. Patten, H. E., and Wag- 

gaman, W. H. Absorption by Soils. U. S. D. A., Bur. Soils, 
Bui. 52. 1908. 



352 SOILS: PROPERTIES AND MANAGEMENT 













y^Ay^Y 


?iOOO 




/ 


^ 


CLAy 


LOAM 


ZOOff 




/ 


^ 


- ^AryoY 


~50/L 


/ooo //y' 


'/y 


^ 








/ 













Fig. 55. — Curves showing the absorption of PO4 in parts to a million 
by various soils from a solution of monocalcium phosphate, contain- 
ing 200 parts to a million of PO4. The volume of the percolate is 
used as the abscissas. 



Nole. — The law which appears to govern absorption of phos- 
phates and potash by the soil may be expressed mathematically 
as follows : — 



dv 



in which iiC is a constant, A the maximum quantity possible 
for the soil to absorb, and y the quantity actually fixed when v, 
volume of the solution, has percolated through. 

A short discussion of the mathematics of this law may be 
found in the following publication : Schreiner, O., and P^xilyer, 
G. H. The Absorption of Phosphates and Potassium by Soils. 
U. S. D. A., Bur. Soils, Bui. 32, pp. 23-24, 37-39. 1906. 



THE ABSORPTIVE PROPERTIES OF SOILS 353 



/OOO/Oyo m 










CLAY 




(,00 




y 










4^0 


/ 


/ 






CLAYlOAn 


^^^ 


zoo / 


/ 


^ 


^>' 




5ANOYS0/L 


-— ' 


/^ 


/ 













■WO 



600 



800 



Fig 



56. — Curves showing the absorption of K in parts to a million by 
various soils from a solution containing 200 parts to a million of K. 
The volume of the percolate is used as the abscissas. 



252. Time required for absorption. — The amount of 
absorption depends on the time of contact between the 
soil and the sokition. While a large part of the dissolved 
base is taken up in a short time after being placed in 
contact with the soil, the maximum absorption is effected 
only after a considerable period. Ammonia, according 
to Way, reaches its maximum absorption in half an hour ; 
while Ilenneberg and Stohmann ^ found that phosphorus 
required twenty-four hours to reach the same degree of 
absorption. 



1 Henneberg, W., and Stohmann. F. Ueber das Verhalten der 
Ackererde gegen Losungon von Ammoniak und Ammoniaksalzen. 
Jour, f . Landw., Neue Folge, Band 3 (Der ganze Reihe siebenter 
Jahrgang), Seite 25-47. 1859. 
2a 



354 SOILS: PROPERTIES AND MANAGEMENT 

This, however, has no sis^nificance so far as danger 
from loss of a soluble fertilizer constituent is concerned, 
since water, even after a heavy rain, would not pass so 
quickly through the soil that absorption would not take 
place, except possibly in the case of soil of a very coarse 
texture. The depth through which the substance is 
distributed in the soil may, however, be influenced by 
the time required for its absorption. Ordinarily ferti- 
lizers do not penetrate very far into the soil. Demolon 
and Bronet ^ have investigated the rate and distance of 
penetration of certain soluble salts in soils, and find that 
a total rainfall of ten inches is not sufficient to carry down 
sodium nitrate in a sandy soil to a depth of eight inches. 

253. Insolubility of certain absorbed substances. — 
Although bases once absorbed may be easily displaced 
by other bases, it is difficult to dissolve them from the 
soil with pure water. Peters - treated 100 grams of soil 
with 250 cubic centimeters of water containing potassium 
chloride, of which 0.2114 gram of K2O was absorbed. 
The soil was then leached with distilled water, using 125 
cubic centimeters of water daily for ten days. At the 
end of that time 0.0875 gram of KoO had been removed, 
or at the rate of 28,100 parts of water to one part of 
K2O dissolved from the soil. Henneberg and Stoh- 
mann ' found that it required 10,000 parts of water 

1 Demolon, A., and Bronet, G. Sur la Penetration des 
Engrais Solubles dans les Sols. Ann. Agron., Tome 28, pp. 
401-418. 1911. 

^ Peters, E. Ueber die Absorption von Kali durch Acker- 
erde. Landw. Vers. Stat., Band 2, Seite 113-1.")1. 1S60. 

^ Henneberg, W., and Stohmann, F. Ueber das Verhalten 
der Aekererde gegen Losungen von Ammoniak und Ammoniak- 
salzen. Jour. f. Landw., Neue Folge, Band .3 (Der ganze Reihe 
siebenter Jahrgang), Seite 25-47. 1859. 



THE ABSORPTIVE PROPERTIES OF SOILS 355 

to dissolve one part of absorbed ammonia from the 
vsoil. 

254. Influence of size of particles. — The surface area 
of the soil particles determines to some extent the amount 
of substance absorbed. For this and other reasons, a 
fine-grained soil absorbs a greater quantity of material 
than a coarse-grained soil. In fact, it was early shown by 
Way ^ that the phenomenon of absorption is largely a 
function of the silt, clay, and humus of the soil. 

255. Causes of absorption. — A number of causes 
have been assigned for the absorption of substances by 
soils, and there can be no doubt that the phenomenon is 
not due to any one process. Several distinct causes are 
now very generally recognized, while others that have 
been suggested may have a part in the result. 

256. Zeolites. — As the result of his extended researches 
on absorption of soils. Way concluded that the property 
of absorption, or fixation of bases, rests largely with the 
hydrated silicates of aluminium, containing calcium or 
magnesium and one of the alkali metals, these compounds 
being known as zeolites. He prepared artificially a 
hydrated silicate of aluminium and sodium, and found 
that by treating this with a solution of a calcium salt 
he could replace most of the sodium, obtaining thereby 
a silicate of aluminium, calcium, and part of the sodium 
that was originally contained in the silicate. The re- 
mainder of the sodium could be replaced by potassium 
from solution and, likewise, by magnesium and ammonium. 

1 Way, J. T. On the Power of Soils to Absorb Manure. 
Jour. Royal Agr. Soc. England, Vol. 11, pp. 313-379. 1850. 
Also, On the Power of Soils to Absorb Manure. Jour. Roval Agr. 
Soe. England, Vol. 13, pp. 123-143. 1852. Also, On the 
Influence of Lime on the " Absorptive Properties " of Soils. Jour. 
Royal Agr. Soc. England, Vol. 15, pp. 491-515. 1854. 



356 SOILS: PROPERTIES AND MANAGEMENT 

Way found further that exposure to a strong heat de- 
stroyed the absorptive properties of these substances, as 
did also treatment with strong hydrochloric acid. In all 
these respects the absorptive properties of the soil and 
of the zeolites coincide. 

257. Chabazite. — Eichhorn ^ experimented with the 
natural zeolite chabazite, and found that he could produce 
substitutions by means of the proper salt solutions. In 
column I of the table below is gi\en the composition of 
chabazite used for the experiment ; in column II is stated 
its composition after treatment with a solution of sodium 
chloride ; and in column III the composition after the 
zeolite is further treated with a solution of ammonium 
chloride : — 

Composition of Chabazite originally and aftek Treat- 
ment WITH Sodium Chloride and afterwards with 
Ammonium Chloride 



Column 


I 


II 


III 


Si02 

A1203 

CaO 

K2O 

NaoO 

H.>0 ....... 

(NH4)20 .... 


47.4 

20.7 

10.4 

0.7 

0.4 

20.2 

0.0 


4S.3 
21.0 
0.7 
O.G 
5.4 
18.3 
0.0 


51.3 

22.2 

4.2 

j 0.6 

14.9 
6.9 



The substitutions were evidently made at the expense 
of calcium in the compound, both when treated with 
sodium and when treated with ammonium salts in chemi- 
cally equivalent cjuantities. These and subsequent ex- 

1 Eichhorn, H. Ueber die Einwirkung Verdiinuter Salz- 
losiingcn auf Ackererde. Landw. Contrlb. f. Deutschland, 
6 Jahrgang, Band 2, Seite 169-175. 1858. 



THE ABSORPTIVE PROPERTIES OF SOILS 357 

periments by numerous investigators have been rather 
widely accepted as indicating that the zeohtes are at 
least partly responsible for the absorptive properties of 
soils. It has been shown further that the absorptive 
power of a soil is more or less proportional to the quantities 
of acid-soluble silicates it contains. The zeolites being 
rather easily soluble in strong mineral acids, it is held 
that the bases so combined are more readily available 
to plants than in most combinations found in the soil, 
and yet are not easily leached out of it. 

258. Presence of zeolites questioned. — On the other 
hand, zeolites have never been definitely proved to be 
present in soils. IMerrill ^ has attempted to show that 
they cannot be of wide occurrence in soils, but neither 
their absence nor their presence has been demonstrated. 
Since the time when Way first published his researches 
in 1850, the zeolite constituents of the soil have generally 
been held to be largely responsible for its absorptive 
power for bases. 

259. Absorption of phosphoric acid. — It has already 
been said that although hydrochloric, sulfuric, and nitric 
acids are not absorbed by soils, except in small quantities, 
phosphoric acid is absorbed and retained in an almost 
insoluble condition so far as extraction with water is 
concerned. That this absorption cannot be due to 
zeolites is generally conceded, and has recently been 
demonstrated, for permutite at least, by Rostworowski 
and Wiegner,^ who in a carefully conducted experiment 

1 Merrill, G. P. Rocks, Rock Weathering, and Soils, pp. 
362-367. New York. 1906. 

2 Rostworowski, S., and Wiegner, G. Die Absorption der 
Phosphorsiiure durch "Zeolithe" Permutite. Jour. f. Landw., 
Band GO, Seite 223-235. 1912. 



368 SOILS: PROPERTIES AND MANAGEMENT 

with this zeolite — Avhich is an amorphous gel containing 
potassium, calcium, aluminium and silicic acid — found 
that there was no absorption of phosphoric acid from a 
neutralized solution of monocalcium phosphate or from 
a solution of dicalcium phosphate at various degrees of 
concentration. 

260. Formation of insoluble phosphates. — The reten- 
tion of soluble phosphoric acid in soils may be easily ac- 
counted for by the fact that there are present in all soils 
hydrated ferric oxide and hydrated silicates of alumina, 
and frequently calcium carbonate, with which substances 
phosphoric acid in solution would naturally form com- 
pounds insoluble in water. Iron and aluminium phos- 
phates are practically insoluble in water containing carbon 
dioxide or weak organic acids such as might be present 
in soil water. Calcium carbonate forms with a soluble 
phosphate fertilizer some dicalcium phosphate, the 
solubility of which in soil water is much greater than 
the iron and aluminium phosphates. This is one of the 
advantages of keeping a soil well supplied with lime if 
a superphosphate fertilizer is to be used. Even the 
tricalcic phosphate, although less soluble than the dicalcic, 
is more readily soluble than the iron and aluminium 
phosphates. As lime has a tendency to move downward 
in soil, and as phosphoric acid is retained in the plowed 
depth when added as a fertilizer, it is important that the 
applications of lime be sufficiently frequent to keep this 
part of the soil in a condition to form the lime phosphates. 

Cameron ^ has suggested that the absorption of })h()s- 
phoric acid is probably due to the formation with lime 
or ferric oxide of a solid solution, which might account 

' Cameron, F. K. The Soil Solution, p. 59. Easton, Penn- 
sylvania. 1911. 



THE ABSORPTIVE PROPERTIES OF SOILS 359 

for the availability of phosphorus in soils to which a 
superphosphate fertilizer had been applied many months 
previously. It might explain also the availability of 
a superphosphate on soils devoid of calcium carbonate. 
Although such availability is always less than where 
this carbonate exists, it is greater than would be ac- 
counted for by the solubility of ordinary iron phosphate. 

261. Adsorption. — There is a physical fixation, termed 
adsorption, due to the concentration of the soil solution 
in immediate contact with the surface of the particles. 
The phenomenon is familiarly exemplified in the clarify- 
ing effect of the charcoal filter. This process results in 
the retention, in fine-grained soils, of considerable soluble 
material that would otherwise be washed out. In the 
case of nitrates, which are not retained by the zeolites, 
adsorption is an important factor (par. 244). If a 
solution of a known quantity of nitrate of soda is added 
to a clay soil, and an attempt is then made to extract 
the nitrate from the soil with distilled water, it will be 
found impossible to recover a very appreciable propor- 
tion of the amount added. While adsorption probably 
does not account for all the nitrates retained, there can 
be no doubt that it plays an important part. Nutritive 
salts held in this way are readily available to the plant, 
whose root hairs come in contact with the soil particles. 
It is not impossible that other fertilizer constituents are 
held by the soil in this manner. 

262. Absorption by colloids. — According to Van Bem- 
melen,' who has made a very exhaustive study of this 

'■ Van Bemmelen, J. M. Die Absorptionsverbindungen und 
das Absorptionsvermogen der Ackererde. Landw. Vers. Stat., 
Band 35, Seite 69-136. 1888. Also, Die Absorption, Seite 
548. Dresden, 1910. 



360 SOILS: PROPERTIES AND MANAGEMENT 

subject, absorption by soils is, without doubt, largely 
due to the presence of colloidal matter which exerts an 
absorbent action for water, gases, solutes, and solids in 
suspension. The colloidal matters in soils that contrib- 
ute to their absorpti\'e proi)erties are the following : — 

(1) remains of plant and animal tissues ; 

(2) humous substances ; 

(3) colloidal iron oxide ; 

(4) colloidal silicic acid ; 

(5) amorphous colloidal silicates that have been formed 

through weathering. 

Van Bemmelen also credits crystalline silicates with 
absorbent properties, although he does not consider that 
their action is Aery important. Absorption is brought 
about also by true chemical combination of soil com- 
pounds with substances in solution, by which certain of 
the cations or anions in solution are chemically combined 
and remain in the soil in a very difficultly soluble condition. 
263. Absorptive properties of colloidal matter. — 
Among the products of rock weathering there have been 
found in soils amorphous substances that are of the nature 
of colloidal gels. These, with the other colloidal matter, 
are contained in the very small particles that remain for 
a long time in suspension when soil is stirred up in water. 
These colloids are coagulated by many acids, and by 
some bases and salts. This is especially true of the 
material that is dialyzable. Some of these again go into 
solution on being treated with water, while others remain 
insoluble until they undergo molecular change. Many 
colloids form hydrogels with soil water. These hydrogels 
are not ordinary chemical compounds. Gels dry very 
slowly. They adsorb water in varying quantities, not 



THE ABSORPTIVE PROPERTIES OF SOILS 361 

in certain definite proportion as do crystalloids in the 
process of crystallization. The more water adsorbed by 
colloids, the less firmly is it held in combination. There- 
fore it is easier to evaporate the water when a large quan- 
tity has been taken up, and as the amount decreases it 
becomes more difficult to drive it off. 

Another property of colloidal matter is that when it 
is separated from solution it carries down with it other 
substances in the solution from which it is precipitated. 
If, on the other hand, the colloidal matter has been pre- 
cipitated in a pure state, it absorbs substances from 
solutions with which it remains in contact for some time. 
The substances taken up in this way are not chemically 
combined, but substances that unite chemically may be 
absorbed. 

The combinations produced by absorption are weak 
and it is possible to leach out the combined substances, 
which are generally held in the water of the gels. The 
following example of one kind of absorption is given 
by Van Bemmelen : ^ ten grams of a hydrogel having the 
composition Si02 . 4.2 H2O, shaken with 100 cubic cen- 
timeter solution of 20 molecular equivalent KCl, will 
absorb 0.8 to 1.1 molecular equivalent of the dissolved 
substance. The absorption in this case was as if the 
solution had been diluted with 4.2 to 5.8 cubic centimeters 
of water. As the amount of gel water in 10 grams of 
hydrogel of Si02 is about 5 cubic centimeters, the as- 
sumption may be made that the dissolved substance is 
taken up in equal concentration by the gel water. Ten 
grams of hydrogel of Si02 shaken with 100 cubic centi- 

^ Van Bemmelen, J. M. Die Absorptionsverbindungen und 
das Absorptionsvermogen der Ackererde. Landw. Vers. Stat., 
Band 35. Seite 75. 1888. 



362 SOILS: PROPERTIES AND MANAGEMENT 

meter solution of 50 molecular equivalent KCl — that 
is, 2^ times the concentration of the former solution — • 
absorbs 2| times as much, or 2.1 to 2.5 molecular equiva- 
lent. This applies also to concentrations five times 
stronger than the first mentioned above, but beyond that 
the relation is not so simple. It serves, however, to 
illustrate the manner in which the abs()rj)ti()n takes place 
from dilute solutions. 

264. Selective absorption. — A selective absorption is 
very common, especially from solutions of salts having 
weak acids, a greater fixation of the bases taking place 
than of the a(;ids. Dissociation of the salts takes place 
in the solution, the bases being absorbed, in consequence 
of which further dissociation occurs ; and this proceeds 
until an equilibrium is established between the absorbing 
and combining power of the colloidal material and the 
reverse action of the water and resulting acids. In this 
way the absorptive power decreases as the amount ab- 
sorbed becomes greater. 

The colloidal silicates possess the property of absorbing 
a certain base when presented to it in solution, and con- 
tributing in return a chemically equivalent quantity of 
some other base. Potassium is most firmly combined 
in the soil and most strongly withdrawn from solution, 
with an exchange of a chemically equivalent quantity of 
calcium, sodium, and magnesium, which passes into the 
solution. If a soil is treated with a solution of potassium, 
magnesium, sodium, or calcium salts of eciual concentra- 
tion, the concentration of the solution in the end is less 
for the potassium than for the magnesium, and Jess for 
the magnesium than for the sodium and the calcium, 
because the potassium is most strongly bound in the 
colloidal material, while the calcium and sodium are least 



THE ABSORPTIVE PROPERTIES OF SOILS 363 

SO. In other words, the action of a calcium salt in solu- 
tion on the absorbed potassium combination is less than 
the action of a dissolved potassium salt on the absorbed 
calcium combination. Thus it comes about that under 
similar conditions of temperature, volume, and concen- 
tration of the solution, the quantity of calcium or of 
sodium or of magnesium that goes into solution when 
colloidal silicates are treated with a solution of a potassium 
salt is greater than the quantity of potassium that would 
go into solution if the same silicates were treated with a 
solution containing the salts of any of these other bases. 

265. Absorptive power of colloidal silicates. — The 
C|uantity of a substance that a certain weight of a colloidal 
silicate can absorb increases with the strength of the 
solution of the substance presented for absorption, be- 
cause the final solution can remain stronger and conse- 
quently its sohent power for that particular substance 
is less. The point of equilibrium between the fixing 
power of the colloid and the solvent action of the solvent 
therefore \'aries with the strength of the solution. 

The nature of the acid with which a base is combined 
likewise has an influence on the quantity of the base 
absorbed. A base combined with a weak acid is ab- 
sorbed in greater amount than the same base combined 
with a strong acid. This is presumably because the 
stronger acid remaining in solution has a greater solvent 
action. 

266. Absorption by colloids versus absorption by 
zeolites. — The early conception of the phenomenon of 
fixation in soils was naturally a chemical one and was 
founded on the chemical knowledge of that day. The 
fact that the substitution of bases in the solutions passed 
through the soil was in chemically equivalent quantities, 



364 soils: pboperties and management 

placed it in line with what was known regardin"^ chemical 
reactions. Zeolites were found to possess absorbent 
properties of a similar nature toward salts in solution, a 
characteristic of which is the substitution of bases and 
the appearance in solution of the released base in com- 
bination with the acid of the original salt. It was a 
natural conclusion that true mineral zeolites exist in 
soil and that the absorptive properties of soil are due to 
their action. 

Many years later, when the principles of physical 
chemistry had been applied to the study of colloids, it 
was shown that absorptive properties are possessed by 
certain colloids similar to those characteristic of soils. 
Zeolites have never actually been isolated from any soil. 
This fact has always occasioned some doubt as to the 
hypothesis to which their properties have given rise. 
Colloids, on the other hand, are well known to occur in soils, 
but the exact nature of soil colloidal matter is not well 
understood ; consequently there is considerable indefinite- 
ness about the extent of their absorptive function, and 
even Van Bemmelen grants the crystalloids a part in this 
phenomenon. 

The zeolite hypothesis furnished an explanation for 
the form in which the available plant-food materials of 
the soil are held. On it is largely based the idea that 
the solution of a soil in strong hydrochloric acid repre- 
sents the nutrients that are available to plants. The 
silicates that go into solution are held to be the zeolitic 
silicic acid and tlie bases with which it is united. The 
fact that such treatment largely destroys the absorptive 
properties of a soil is taken as a proof of this. It would, 
however, answer equally well as an argument in favor 
of colloidal absorption, as the colloidal condition of the 



THE ABSORPTIVE PBOPERTIES OF SOILS 365 

silicates would be destroyed by the same treatment. 
On the whole, the evidence appears to be in favor of 
the dominance of colloidal absorption rather than 
crystalloidal absorption by soils, with its important 
function in conserving soluble fertilizers and retaining 
a supply of plant nutrients in a more or less readily 
available condition. 

267. Absorption by organic matter. — The partially 
decomposed organic matter in soils, especially that part 
which has undergone such transformations as to form 
humus (par. 90), has an absorptive power. Soils rich 
in humus, without doubt, owe much of their fertility 
to the retention by that constituent of a large supply of 
readily available plant-food material. Many prairie soils 
that have been reduced in productiveness under culti- 
vation respond to the application of organic matter in a 
remarkable manner. Humus in these soils seems to be the 
chief conserver of readily available plant-food materials. 

Van Bemmelen/ who has studied these compounds, 
states that soils hold colloidal humous compounds con- 
taining ammonia, potassium, sodium, and other sub- 
stances, as well as iron oxide. A part is soluble, or forms 
soluble compounds with alkalies, but the principal part 
is insoluble. Some of these latter compounds are of a 
colloidal nature and of changing composition. The soluble 
matter is easily precipitated by a salt solution and carries 
down with it bases from the solution. Absorption of bases 
also takes place from solution, with substitution of one 
base for another. Potassium is more strongly held in 
combination than is calcium or magnesium. Bases are 
removed, however, only from salts of the weaker acids. 

^ Van Bemmelen, J. M. Die Absorption, Seite 135-141. 
Dresden, 1910. 



366 SOILS: PROPERTIES AND MANAGEMENT 

268. Absorption of water vapor and of gases by soils. — 
Hygroscopic water in soils has already been fliscussed (pars. 
133, 134, 135). It need merely be remarked here that 
there is a close relation between the absorptive power of a 
soil for water vapor and for bases. Soils having a high 
content of humus and composed of very fine material are 
likely to have great absorptive properties for both vapors 
and solutes. 

In a similar way soils absorb gases. The deodorizing 
property of soil is well known. Decomposing organic 
matter is rendered inoffensive by covering it with soil. 
Gases produced in the processes of decomposition are 
largely absorbed by the soil. The fertility of the soil 
may be increased by the absorption of certain gases. 

269. Absorption of ammonia. — Ammonia, which exists 
in minute quantities in the air, is absorbed by soils, and 
also when given off by decomposing organic matter in the 
soil. As all nitrogeneous organic matter may eventually 
form ammonia when decomposed, the ability of the soil 
to absorb it is very important. Quartz alone will absorb 
only a very small quantity of ammonia, while a clay soil 
will hold practically all that is likely to be produced by 
the decomposition of the organic matter incorporated in it. 

270. Absorption of carbon dioxide. — Carbon dioxide 
is absorbed by soils to a very considerable extent, and 
this also adds to the productiveness of soils, since it aids 
in their decomposition. The supply of carbon dioxide 
comes from decomposing organic matter and from plant 
roots. As will be explained later, the soil air always 
contains a considerable supply of this gas, and its con- 
densation and absorption is constantly going on. It 
forms soluble bicarbonates with the alkalies antl bases 
of soils, producing a readily available plant-food material. 



THE ABSORPTIVE PROPERTIES OF SOILS 367 

271. Absorption of nitrogen and oxygen. — Nitrogen 
is absorbed })y soils to a greater degree than is oxygen. 
The latter probably is of greater importance to soil fer- 
tility, as its absorption is accompanied by oxidation of 
other absorbed gases. Because of their absorptive prop- 
erties and their great surface area, soils have strong 
oxidizing power. 

The absorption of gases by soils is largely an absorp- 
tion phenomenon, the gases being condensed on the 
surface of the particles. Von Dobeneck ^ has shown 
that the absorption is greater, the finer the particles 
of soil ; but this increase is not directly proportional 
to the increase in surface, large particles apparently 
having a greater adsorptive power than their surface 
area would indicate. 

272. Relation of temperature to gas absorption. — 
The temperature of the soil influences its absorptive 
pro})erties for vapors. As the temperature increases the 
absorption becomes less. Hilgard ^ does not find this 
to be the case (par. 136). He exposed soils to a moisture- 
saturated atmosphere and found that they absorbed 
more moisture at high than at low temperatures. In 
his conclusions, however, he is doubtless in error. All 
the work previous to his gave a directly contrary result, 
and a more recent investigation by Patten and Gallagher ^ 
confirmed the work of the earlier investigators. 

1 Von Dobeneck, A. F. Untersuchungen iiber das Adsorp- 
tionsvermogen und die Hygroskopizitat der Bodenkonstit- 
uenten. Forsch. a. d. Agri.-Physik., Band 15. Seite 163-228. 
1892. 

2 Hilgard, E. W. Soils, pp. 196-198. New York, 1906. 

' Patten, H. E., and Gallagher, F. E. Absorption of Gases 
and Vapors by Soils. U. S. D. A., Bur. Soils, Bui. 51, pp. 31- 
35. 1908. 



368 SOILS: PROPERTIES AND MANAGEMENT 

273. Relation of absorptive capacity to productiveness. 

— The absorptive capacity of a soil is not so much a 
measure of its immediate as of its permanent i)roductive- 
ness. It is well known that a very sandy soil responds 
quickly to the application of soluble manures, but that 
the effect is confined mainly to one season ; while a clay 
soil, although not so quickly responsive to fertilization, 
shows the effect of the application much more markedly 
the second or the third year than does the sandy soil. 
Adsorption, which is largely shown in sandy soil, holds 
the nutritive material in a \'ery readily available con- 
dition, while absorption by amorphous compounds 
renders these substances somewhat less readily available. 
There are also other reasons why the sandy soil is more 
responsive. King,^ in working with eight types of soil 
from different parts of the United States, found that 
those soils removing the most potassium from solution 
gave the largest yield of crops. It would not be per- 
missible, however, to adopt this test as a method for 
determining productiveness in soil. 

274. Absorption as related to drainage. — The drainage 
water from cultivated fields in humid regions, and to a 
less extent in semiarid and arid regions, except where 
irrigation is practiced, carries off very considerable quan- 
tities of plant-food material. Tlie loss of this material 
is due to the operation of the various natural disintegrating 
agents on the soil mass, and to the application of fertilizing 
materials in a soluble form. The various absorptive prop- 
erties stand between the natural solubility of the soil and 
the tendency to loss in drainage, and hold, in a condition 

* King, F. IT. Influence of Farm Yard Manure upon Yield 
and upon the Water-Soluble Salts of Soils, p. 25. Madison, 
Wisconsin. 1904. 



THE ABSORPTIVE PROPERTIES OF SOILS 360 

in which they may readily be used by the plant, these 
materials which would otherwise be lost. 

275. Substances usually carried in drainage water. — 
However, some material is always lost in drainage water, 
of which, among the bases of the soil, those most likely to 
be found are calcium, sodium, magnesiiun, and potassium ; 
and of the acids, carbonic, nitric, sulfuric, and hydrochloric. 
Nitric acid and lime undergo the most serious losses. 
The former may be curtailed to a great extent by keeping 
crops growing on the soil during all the time that nitri- 
fication is going on, and if the crop does not mature, or 
if for any other reason it is not desired to harvest the 
crop, it should be plow^ed under, to return the nitrogen in 
the form of organic matter. A crop used for this purpose 
is called a catch crop. Rye is used rather commonly as 
a catch crop, as it continues growth until late in the fall 
and resumes gro^^i:h early in the spring, conserving ni- 
trates whenever nitrification is likely to occur, and 
it may then be plowed under to prepare the land for 
another crop. Rye also has the advantage of small 
cost for seed. 

The loss of calciiun cannot w^ell be prevented, and 
the use of commercial fertilizers always greatly increases 
such loss. The only remedy is the application of some 
form of calciiun to the soil. 

276. Drainage records at Rothamsted. — Drainage 
water from a series of plats at tlie Rothamsted Experi- 
ment Station, which have been manured in various 
ways and planted to wheat each year since 1S52, have 
been analyzed at certain times, and the results of these 
analyses, as compiled by Hall,^ give some idea of the loss 

' Hall, A. D. The Book of the Rothamsted experiments, 
pp. 237-239. New York, 1905. 
2b 



870 SOILS: PROPERTIES AND MANAGEMENT 

of salts from cultivated soils. The draina<2;e water was 
obtained from the tile drains, a line of which extended 
mider each plat from one end to the other and opened 
into a ditch, so that the water could be collected when 
desired. The analyses are shown in the table on page 
371. 

Ammoniacal nitrogen in the drainage water is very small 
in quantity, but nitrate nitrogen is present in quantities 
sufficient to make the loss of some concern. The use of 
sodium nitrate occasioned the greatest loss of nitrogen, 
w^hile ammoniiun salts and farm manure contributed 
nearly as much. From forty to fifty pounds of nitrogen to 
the acre may be lost annually in this way; this amount 
would hnxe a commercial value of eight or nine dollars. 

277. Drainage records at Bromberg. — It is not 
always the case that a manured soil loses more fertilizing 
material than an unfertilized one. Gerlach ^ reports 
experiments in soil tanks at the Bromberg Institute of 
Agriculture, as the result of which five soils, when ration- 
ally fertilized, yielded larger crops and lost in the main 
less nitrogen and lime in the drainage water than the 
same soils unmanured. The loss of potash was slightly 
greater from the manured than from the unmanured soils. 
Apparently the stimulation that the plants received 
from the fertilizer enabled them to make such a good 
growth that they absorbed more soluble nitrogen and 
lime in excess of the unfertilized plants than was added 
in the fertilizer, and nearly as much potash. 

1 Gerlacli, M. Ueber die durch Siekerwasser dem Boden 
Entzogenen Menge Wasser und Nahrstoffe. Illus. Landw. 
Zeitung, 30 Jahrgang, Heft 95, Seite 871-881. 1910. Also, 
Untersuchungen iiber die Mengc und Zusammensetzung c^er 
Siekerwasser. Mitt. K. W. Inst. f. Landw. in Bromberg, Band 
3, Seite 351-381. 1910. 



THE ABSORPTIVE PROPERTIES OF SOILS 371 



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372 SOILS: PROPERTIES AND MANAGEMENT 

278. Losses of nitrogen and calcium. — The most 
serious losses of pluiit nutrients in the (lrainafi;e water of 
soils are those of nitrogen and calcium, and both are to 
an extent unavoidable. Potassium and phosphorus, 
which must also be purchased in manures, are lost only 
at the rate of a few pounds to the acre. Nitrogen and 
calcium may be conserved by maintaining a crop on the 
soil continually. A large removal of nitrogen in the 
drainage water is usually accompanied by a large re- 
moval of calcium ; for nitrogen is leached from the soil 
mainly in the form of nitric acid, which of course com- 
bines with a base, and calcium being the base finally 
liberated it is carried off in drainage water. While most 
of the calcium in drainage water is in the form of bicar- 
bonate, the quantity is greatly increased by nitric acid. 

The relation of nitric acid to calcium in drainage water 
is shown by experiments with soil in large tanks from which 
drainage water was collected. Plants were grown in the 
soil of certain tanks, while others had none, other conditions 
being similar. Analyses of the drainage water at Ithaca, 
New York, as reported by Lyon and BizzelH show a greatly 
increased loss of calcium from the unplanted tanks, from 
which the loss of nitrate nitrogen was also much greater : — 

Nitrogen and Calcium Removed in Drainage Water be- 
tween May 2.3, 1910, axd May 1, 1911. Calculated to 
Pounds to the Acre 



Crop Grown 


Nitrate Nitrogen 


Calcium 


None 

INIaize 

Oats 


119.6 
10.8 
12.5 


406.7 
1.58.0 
173.4 



1 Lyon, T. L., and Bizzell. J. A. Composition of the Drain- 
age Water of a Soil with and without Vegetation. Jour. Indus, 
and Eng. Chem., Vol. 3, pp. 742-743. 1911. 



THE ABSORPTIVE PROPERTIES OF SOILS 373 

Where crops were present to absorb the nitric acid, 
calcium was greatly conserved. The quantities of ma- 
terial carried off in drainage water was doubtless ab- 
normally high in this case, as the soil had recently been 
placed in the tanks. 

279. Composition of surface wat^r. — ■ Another method 
proposed for obtaining these data is to analyze and 
measure the water draining from a known area of land. 
Norton ^ has done this in the valley of Richland Creek, 
Arkansas, and has calculated the loss of a number of the 
soil constituents. A comparison of the figures obtained 
by Norton with those obtained by Lyon and Bizzell in 
the experiments just quoted will give some idea of the 
quantities of mineral matter removed from soils by 
drainage water. The Arkansas soil had presumable- 
received little manure. The soil in the Cornell Uni- 
versity tanks had previously received fifteen tons of 
stable manure. The Arkansas drainage doubtless in- 
cluded some surface water that had never passed through 
the soil and was therefore poor in mineral matter; the 
large quantity of volatile matter indicates its surface 
nature, as w-ater that passes through a soil contains little 
organic matter. 

There is little similarity in the results of these analyses. 
They serve, however, to bring out the differences between 
the composition of the run-off and the drainage water of 
soils, in so far as that may be judged from widely dif- 
ferent soils and climatic conditions, including the 
rainfall, 

1 Norton, J. H. Quantity and Composition of Drainage 
Water and a Comparison of Temperature, Evaporation, and 
Rainfall. Journal Am. Chem. See., Vol. 30, pp. 1186-1190. 
1908. 



374 .^OILS: PROPERTIES AND MANAGEMENT 



Substances Removed in Drainage Water from One Acre 
OF Land in One Year 





Norton 


Lyon and Bizzell 




Planted Soil 


Bare Soil 


• 
Total solids .... 
Organic matter . . . 

Nitrogen 

Potash 

Phosphoric acid . . . 
Lime 


794.0 

134.0 

4.0 

5.0 

0.1 

81.0 


800 



11 

6 

Trace 
158 


2584 



119 

11 

Trace 
407 



It will be seen that the total solids in the drainage 
water from the Arkansas land and from the planted 
tank were not greatly different in amount, but that 
none of the constituents differed greatly. This was 
notably the case with organic matter and with lime. 
The former was doubtless carried largely in the run-oft' 
and not in the leachings. The latter was probabl}'^ more 
abundant in the glaciated soil used in the tank than 
in the residual soil of Arkansas. 



CHAPTER XVII 

ACID, OR SOUR, SOILS 

Some soils are known as acid, or sour, soils. The 
property of acidity is of practical significance because 
some plants do not grow so well on sour soils as they do 
on soils that are neutral or alkaline ; on the other hand, 
some crops prefer an acid soil. Sour soils are rarely met 
with in arid regions, but in humid sections of the United 
States they are commonly found. 

280. Nature of soil acidity. — Soils may be acid, or 
sour, so far as their relation to plant growth is concerned, 
(1) when free acids are present, (2) when no soluble free 
acid exists, but when there is a deficiency of basic material 
in the soil. Decomposition of organic matter in certain 
soils under an inadequate supply of oxygen often results 
in the formation of considerable quantities of organic 
acids, as has already been explained (par. 93). 

281. Positive acidity. — The formation of organic 
acids under conditions of insufficient oxygen supply is 
frequently' seen in muck and other soils high in organic 
matter that are saturated with water and that are also 
deficient in lime. In such cases an acid condition is very 
likely to be found, but when the land is drained the 
acidity usually disappears because of the better aeration 
resulting. When a large quantity of green vegetation 
is plowed under, as is done in green-manuring land, a 
sour condition sometimes appears after the material has 

375 



376 SOILS: PROPERTIES AND MANAGEMENT 

had time partially to decay. The acidity of soil that 
arises from the presence of free acids has been termed 
positive acidity. 

It is to be presumed that soils in which free acids exist 
are rather deficient in basic material, and that the bases 
are held so firmly combined that some of the relatively 
weak organic acid present is not capable of forming salts 
with them. Plummer ^ has shown that dihydroxy stearic 
acid when added to an acid soil had a distinctly toxic 
effect on wheat plants, but when added to the same soil 
previously treated with lime there was no toxic effect, 
indicating that this substance retained its acid properties 
in the unUmed soil. 

282. Negative acidity. — A soil deficient in basic 
material but containing no soluble free acids may be 
sour as regards its relation to plant growth. At least 
such a soil may be greatly benefited by liming, although 
it shows no acidity to most of the ordinary indicators of 
acidity when these are used in the customary way. This 
condition has been termed negative acidity and is really 
not acidity according to a correct use of the word. Such 
acidity does not have a direct effect on the plant, but 
an indirect one arising from a lack of bases. Soils that 
are acid in this sense always have a large capacity for 
absorbing lime or other bases, before exhibiting an al- 
kaline reaction. Calcium being, as has already been 
seen (par. 264), the base most liberally released to solution, 
there is a tendency toward the formation of calcium 
carbonate in any soil dependent on the equilibrium be- 

1 Plummer, J. K. The Isolation of Dihydroxystearip Acid 
from Volusia Silt Loam. Thesis presented in partial fulfillment 
of the requirements for the degi-ee of Master of Science. Cornell 
University Library (not published). 191L 



ACID, OR SOUR, SOILS 377 

tween the basic material and the absorptive substances 
in the soil. Thus, a soil containing large quantities of 
clay, and other absorbent substances requires more basic 
material for the formation of calcium carbonate than 
does a soil having less absorptive material. Further- 
more, with the same original content of basic material, 
the former soil requires a greater addition of lime to 
overcome its sourness than does the latter. For this 
reason a heavy soil usually requires a larger dressing of 
lime to correct its acidity than does a light one. 

Even if a soil does not have its absorptive capacity for 
bases satisfied, there is some formation of calcium car- 
bonate constantly taking place, as is evidenced by the 
removal of the bicarbonate of calcium in the drainage 
water of soils that are distinctly acid. The benefits that 
soils derive from the presence of calcium carbonate will 
be mentioned later (pars. 454-457) . It need only be said 
here that its presence in insufficient quantity constitutes 
a form of so-called acidity, or sourness, in soils. The 
formation of calcium carbonate in a given soil increases 
with the mass of base. The effect of an application 
of lime, therefore, is to increase the quantity of car- 
bonate formed, even w^hen the absorptive capacity of 
the soil is not satisfied. This is why even relatively 
small applications of lime are beneficial to soils having 
great absorptive capacity. 

283. Production of sour soils. — Soils in a humid 
region tend to become acid. This may be due to anj'^ one 
or more of several causes: (1) removal of calcium and 
other bases in drainage water; (2) removal of bases by 
plants; (3) formation of salts of the bases with organic 
matter incorporated with soil; (4) accumulation of acid 
residues of fertilizers. 



378 SOILS: PROPERTIES AND MANAGEMENT 

284. Removal of bases by drainage as a cause for 
acidity. — The most potent cause of acid soils is doubt- 
less the removal of bases in drainage water. The quan- 
tities of basic material that may be lost from an acre of 
soil are shown elsewhere (pars. 278, 279). These bases are 
removed largely as bicarbonates, being obtained from 
the hydrated aluminium silicates and other colloidal 
matter. When the soil is uncropped a considerable loss 
of lime occurs in the form of nitrate. As the decom- 
position of the organic matter of the soil always results 
in the formation of carbon dioxide and nitric acid, and 
as decomposition is continually going on except when the 
temperature of the soil becomes too low to admit of it, 
the drain of bases from the soil is almost continuous. 
Formation of carbon dioxide and of nitric acid occurs 
largely in the surface soil ; consequently the removal 
of bases begins there. The result is that soils are 
likely to contain less calcium in the surface layers than 
at lower depths. Ames and Gaither ^ have shown from 
a large number of analyses of Ohio soils that those con- 
taining calcium carbonate in appreciable quantities have 
more calcium in the subsoil than in the surface sLx 
inches. In other soils this was not uniformly the case. 
Leaching is, of course, greater in amount where con- 
siderable quantities of calcium carbonate are present 
than where it is lacking. 

285. Removal of bases by plants. — Plants always 
remove more bases than acids from soils in the process 
of their growth. The table in paragraph 339 showing the 
composition of the ash of some crops indicates that the 
calcium, potassium, and magnesium removed from 

» Ames, J. W., and Gaither, E. W. Soil Investigations. 
Ohio Agr. Exp. Sta., Bui. 201. 1913. 



ACID, OR SOUB, SOILS 379 

the soil in this way is very considerable. When the 
vegetation on the land is returned to it after life 
ceases and its organic material is again incorporated 
with the soil, there is no loss in this way, but in ordi- 
nary agricultural practices most of the above-ground 
portion of the crops is removed from the land. The 
manure of growing animals returns to the soil only a 
small proportion of the calcium that was originally in 
the plants. 

Breazeale and LeClerc ^ found that the selective action 
of plants in absorbing more bases than acids from a 
nutrient solution caused the solution to become toxic to 
wheat seedlings because of its acidity. 

286. Effect of green manures on acidity. — Although 
the return of vegetation to the land on which it grew 
does not result in any actual loss of basic material to 
the soil, it generally results in the formation and libera- 
tion of organic acids that unite with the basic material 
and thus render it neutral. In soils deficient in lime 
the incorporation of green-manure crops has been con- 
sidered to temporarily produce an acid condition. 
Coville - determined the acidity of some green-ma- 
nure crops, on the basis of which he has estimated 
the acidity, in terms of ground limestone required to 
neutralize it, when the lime contained in the crop is de- 
ducted from the total lime required. This is given in the 
table on the next page. 



1 Breazeale, J. F., and LeClerc, J. A. The Growth of Wheat 
Seedlings as Affected by Acid or Alkaline Conditions. U. S. 
D. A., Bur. Chem., Bui. 149. 1912. 

^ Coville, J. V. The Agricultural Utilization of Acid Lands 
by Means of Acid-Tolerant Crops. U. S. D. A., Bui. No. 6, 
p. 5. 1913. 



380 SOILS: PROPERTIES AND MANAGEMENT 



Weight, Lime Contknt, and Acidity of Green Manures 
TO THE Acre 





Crop 


, Weight 
(tons) 


Lime 
Content 
(pounds) 


Acidity, ex- 
pressed AS Lime 
Requirement 
(pounds) 


Alfalfa 

Red clover .... 

Cowpea 

Rye 

Broom sedge .... 


2^ 
2 

2^ 

2 

1 


139 

131 

92 

11 

4 


267 

142 

200 

178 

89 



As decomposition proceeds the acids are oxidized, and 
finally basic material is held largely in combination with 
so-called humus of the soil. This is doubtless in the 
form of a colloidal complex, not a definite chemical com- 
pound. Analyses by Snyder ^ of purified hiunous ash 
from eight productive prairie soils have been averaged 
and are presented in tabular form in paragraph 97. 

The quantity of basic material ordinarily held by the 
organic matter of the soil is small compared with the 
total soil content. The bases contained in h inn us are 
principally potassium and sodium — not calcium, as 
might be expected in the salt of an organic acid formed 
in the soil. Hmnus in the soil tends to overcome acidity 
and functions as an alkali. In respect to its composition 
and properties, much of it resembles a colloidal com- 
plex rather than a chemical combination of soil bases 
with organic acids. 

It has often been observed that land from which forest 
has been cleared will yield good crops of red clover for 



^ Snyder, Harry. 
41. 1895. 



Soils. Minnesota Agr. Exp. Sta., Bui. 



ACID, OR SOUR, SOILS 381 

several decades, after which it becomes more and more 
difficult to obtain a crop until the attempt must finally 
be abandoned. The change from forest to tillage has 
opened the way for an acid condition of soil, through the 
loss of bases carried off in the crops and the destruction 
of humus by tillage. The dissipation of humus is doubt- 
less the more serious source of loss. Instances may be 
cited in which a farm has been so managed as to main- 
tain the humus supply and the ability of the soil to pro- 
duce red clover, although surrounding farms, on which 
humus has been depleted, have completely failed to grow 
this crop. 

Apparently humus holds the basic constituents of the 
soil in a form in which they function as rather easily 
soluble salts, instead of locking them up as insoluble 
silicates. A given quantity of base in a soil is therefore 
more effective in preventing acidity by combining with 
weak acids, and possibly in forming carbonates, if the soil 
is well supplied with humus than if it is lacking in that 
constituent. 

287. Effect of fertilizers on soil acidity. — That the 
continued use of ammonium sulfate on land may result 
in producing a sour condition has been shown by a num- 
ber of investigators. The absorption and nitrification 
of the ammonia of that salt, and its final utilization by 
plants, leaves sulfuric acid, which combines with calcium 
and escapes in the drainage water. This may occur even 
when this fertilizer is used in quantities not excessive, 
but continued for many years, as has been shown by 
Gardner and Brown ^ at the Pennsylvania Experiment 

* Gardner, F. D., and Brown, B. E. The Lime Require- 
ment of the General Fertihzer Plats as Determined Periodically. 
Rept. Pennsylvania Agr. Exp. Sta., 1910-1911, pp. 25-60. 



382 soils: properties and management 

Station. Other fertilizers leaving an acid radicle in the 
soil also act in this way. It is conceivable that potassium 
chloride and potassium sulfate might have a tendency 
to produce an acid condition, but the bases in these salts 
do not disappear from the soil so quickly as would am- 
monia, and consequently their action is slower. 

The use of free sidfur on the land as a means of com- 
bating certain fungous diseases may lead to the formation 
of a sour soil through the oxidation of the sulfur with 
formation of sulfuric acid. Lint ^ has found that a 
soil in which sulfur was used at the rate of (iOO pounds 
to the acre for prevention of potato scab, changed in its 
lime requirement from 2431 pounds to 4177 pounds as a 
result of the one treatment. 

288. Acidity in relation to climate and to formation of 
soil. — In an arid or a semiarid climate soils are not likely 
to become sour. The great source of lime removal, 
leaching, operates to only a slight extent, or not at all, 
in a dry climate. The removal of bases in crops is ap- 
parently offset by the upward movement of bicarbonates 
in the capillary w ater. Experience shows that acidity is 
not a problem in soils of dry countries. 

Soils that are derived from limestone or that have been 
mixed with limestone soils in the process of their forma- 
tion are, under similar climatic conditions, less likely 
to become acid than are soils that originally contained 
less lime. The fact that a soil is derived from limestone, 
however, does not insure that it may not be benefited by 
an application of lime. 

289. Weeds that flourish on sour soils. — The acidity 
or the basicity of soils influences very greatl>' the growth 

' Lint, H. Clay. The Influence of Sulfur on Soil Acidity. 
Jour. Indus, and Eng. Chem., Vol. 6, pp. 747-748. 1914. 



ACID, OR SOUR, SOILS 383 

of vegetation and determines to a large degree its nature. 
The flora undergoes a considerable variation as a soil 
changes from a basic to a sour condition. This is because 
some plants are injured to a greater extent than are others 
by the conditions that accompany an acid reaction of the 
soil. Some higher plants really grow better on a sour 
soil than they do on an alkaline one, but these form only 
a minority of the plants of agricultural importance. 
Weeds that abound and appear to flourish on acid soils 
may do so either because they grow better on sour soil 
than on basic, or because other vegetation growing on 
the soil does not thrive and therefore the dominant weeds 
of the region have less competition than they otherwise 
would have. There are certain weeds that may be taken 
to indicate a sour soil when present in large numbers. 
Some of these are found in one part of the country and 
some in another : — 

Weeds that Flourish on Sour Soils 
Common name Botanical name 



Sheep sorrel ^ . 
Paintbrush . . 
Daisy . . . 
Horsetail rush ^ 
Corn spurry ^ . 
Wood horsetail ^ 
Plantain ^ . . 
Goose grass ^ 



Rume.v acetosella 
Hieracium aurantiacum 
Bellis yerennis 
Equisetum arvense 
Spergula arvensis 
Eqmsetum syhaticum 
Plantago major 
Polygonum aviculare 



1 Knisely, A. L. Acid Soils. Oregon Agr. Exp. Sta., Bui. 
90, p. 23. 1906. 

2 Whitson, A. R., and Weir, W. W. Soil Acidity and Liming. 
Wisconsin Agr. Exp. Sta., Bui. 2.30, pp. 7-11. 1913. 

' Voelcker, J. A. The Woburn Field Experiments. Jour. 
Royal Agr. Soc. England, Vol. 69, pp. 337-357. 1908. 



384 SOILS: PROPERTIES AND MANAGEMENT 

290. Crops adapted to sour soils. — There are some 
useful agriculturul plants that j:jrow better on sour soils 
than on alkaline soils, while other plants are apparently 
indifferent to the condition of the soil in this respect. As 
acid soils are of very common occurrence, and as the 
correction of this difficulty may not always be financially 
profitable or otherwise desirable, it is important to know 
what plants will thrive and how agricultural practice 
may be maintained on such soils. A list of these plants, 
based on different authorities, is herewith given : — 

Crops Adapted to Sour Soils 

Blueberry ^ Hairy vetch ^ 

Cranberry ^ Crimson clover ^ 

Strawberry ^ Potato '^ 

Blackberry ^ Sweet potato ^ 

Raspberry ^ Rye ^. 

Blackcap ^ Millet 2 

Watermelon ^ Buckwheat ^ 

Turnip ^ Carrot ^ 

Red top - Lupine - 

Rhode Island bent-grass ^ Serradella ^ 

Cowpea ^ Radish - 

Soybean ^ ^'elvet bean ^ 
Castor bean ^ 

The very considerable number of these plants, and 
especially the inclusion among them of legumes that 
may be grown for soil impro\'ement, suggest the possi- 

1 Coville, F. W. The Agricultural Utilization of Acid Lands 
by Means of Acid-Tolerant Crops. U. S. D. A., Bui. No. 6, 
pp. 7-12. 1913. 

2 Wheeler, H. J. The Liming of Soils. U. S. D. A., Farmers' 
Bui. 77. 1905. 



ACID, OB SOUR, SOILS 



385 



bility of a successful agricultural practice on acid soils 
where the important money crop to be grown, or some 
other condition, would make it undesirable to correct 
the soil acidity. There are certain crops, such as blue- 
berries and cranberries, that require an acid soil ; there 
are others, such as potatoes, that may suffer less from 
disease if the soil is sour. These crops are sometimes the 
ones that are of greatest financial importance in a region, 
and it therefore becomes desirable to maintain an acid 
condition of soil. 

291. Crops that are injured by acid soils. — There 
are many plants that are injured by a sour condition of 
the soil, and these include some of the most important 
farm crops. It should therefore be borne in mind that 
for most farm practice an acid soil is very undesirable. 
One notable reason for this is that such crops as red 
clover and alfalfa, which are of great value both as a 
means of improving soil and for hay, can be grown only 
with great uncertainty or not at all on acid soils. 

Crops that are Injured by Sour Soils' 



Alfalfa 


Salsify 


Cauliflower 


Red clover 


Squash 


Cabbage 


Saltbush 


Spinach 


Cucumber 


Timothy 


Red beet 


Lettuce 


Kentucky blue-grass 


Sorghum 


Onion 


Maize 


Barley 


Okra 


Oats 


Sugar beet 


Peanut 


Pepper 


Currant 


Tobacco 


Parsnip 


Mangel-wurzel 


Kohlrabi 


Pumpkin- 


Celery 


Eggplant 



1 Wheeler, H. J. The Liming of Soils. U. S. D. A., Farmers' 
Bui. 77 (revised). 19a5. 
2c 



386 SOILS: PROPERTIES AND MANAGEMENT 

While soils may be either sour or alkaline, there are 
also degrees of sourness. Thus a soil may be so sour as 
to completely prevent the growth of one kind of plant 
and yet produce excellent crops of another plant which 
would have perished if the soil had been more acid. For 
example, red clover will grow fairly well on soil that is 
too sour to raise alfalfa. 

292. Qualitative tests for acidity. — A simple test to 
indicate an acid condition of soil is not so easy of execu- 
tion nor so infallible in its prediction as might be desired. 
The object of such a test is to ascertain whether a soil is 
not well adapted to the growth of certain plants and 
whether the application of lime would benefit it in this 
respect. A number of tests have been proposed which 
will be outlined and briefly discussed. 

293. Litmus paper test. — Blue litmus paper is brought 
into contact with the wet soil. A rapid and decided 
change to red is taken to indicate an acid condition of 
the soil. Carbonic acid, which is always present in soils, 
is supposed to give only a faint pink color to the litmus 
paper. Various ways of bringing the paper into contact 
with the soil have been recommended, among others the 
interposing of filter paper between the soil and the litmus 
paper. ^ It is also generally pointed out that the acid 
perspiration on the fingers may lead to delusion. 

A criticism of the test has been made by Cameron,^ 
who states that the absorbent action of soils for bases is 
greater than is that of paper, while for acids the reverse 

1 Kellerman, K. F., and Robinson, T. R. Legume Inoculation 
and the Litmus Reaction of Soils. U. S. D. A., Bur. Plant Indus., 
Circ. 71, pp. 3-11. 1910. 

2 Cameron, F. K. The Soil Solution, pp. 65-GG. Easton, 
Pennsylvania. 1911. 



ACID, OR SOUR, SOILS 387 

is the case. Consequently the base that had produced 
the blue color is absorbed from the litmus, leaving the 
acid compound, which is red. Cameron concludes that 
the test is unreliable, and proposes to extract the soil 
with water, boil it in order to expel carbon dioxide, and 
then test the reaction of the solution. 

Much litmus paper that is sold is of very poor quality ; 
but when good paper is used and the test is carefully 
made, the general experience has been that it is a fairly 
good, although not an infallible, guide to the need of a 
soil for lime. Red coloration due to absorptive action is 
probably an advantage rather than a source of error in 
the test, as a soil strongly absorptive of bases is likely 
to need lime. This coloration does not necessarily in- 
dicate the presence of free acid, but merely need of lime. 

294. Ammonia test. — In this test the soil is stirred 
with a dilute solution of ammonia hydroxide. After 
settling, if the supernatant liquid on standing takes on 
a dark chocolate or a black color it is said to be acid. 
This method, which has been proposed by Miintz,^ is 
not of general application and would not always be re- 
liable in the case of soils of arid regions. The depth of 
color is not a guide to the degree of acidity, since many 
acid soils are low in organic matter. 

295. Zinc sulfide test. — A test recently proposed by 
Truog ^ consists in mixing the soil to be tested with a 
small quantity of calcium chloride and a very little zinc 
sulfide. Water is added and the mixture is heated to 



1 Wheeler, H. J., Hartwell, B. L., and Sargent, C. L. Chemi- 
cal Methods for Ascertaining the Lime Requirements of Soils. 
Rhode Island Agr. Exp. Sta., Bui. 62, pp. 6.5-88. 1899. 

^ Truog, E. A. New Method for the Determination of Soil 
Acidity. Science, N. S., Vol. 40, pp. 246-248. 1914. 



388 SOILS: PROPERTIES AND MANAGEMENT 

boiling. A strip of moistened lead acetate paper is held 
over the mouth of the flask for two minutes while the 
boiling proceeds. If the soil is acid, the paper will be 
darkened on the underside ; if the soil is not acid, no 
darkening will occur. 

This method is evidently designed to test the need of 
the soil for lime as well as actual acidity, for the absorp- 
tion of calcium from the dissociated chloride would leave 
free hydrochloric acid. The action of this acid on zinc 
sulfide would generate hydrogen sulfide, thus blackening 
the lead acetate paper. 

A somewhat similar principle is involved in the proposal 
to use a solution of potassium nitrate in the litmus paper 
test. 

296. Litmus paper and potassium nitrate. — This is 
performed in the same manner as the former litmus 
paper test, except for the substitution of a saturated 
solution of potassium nitrate instead of distilled water 
for moistening the soil. 

297. Acid test for carbonates. — In this test a dry 
sample of the soil is treated with a few drops of dilute 
hydrochloric acid. Effervescence indicates the presence 
of carbonates or bicarbonates in sufficient quantities to 
insure an alkaline soil, although sometimes lime may 
still be beneficial. 

Whitson and Weir ^ have objected to this method on 
the ground that the displacement of air in the pore spaces 
of the soil by the dilute acid may be mistaken for evolu- 
tion of carbon dioxide. In the hands of an experienced 
and careful operator this would not necessarily invalidate 
the method. 

• Whitson, A. R., and Weir, W. W. Soil Acidity and Lim- 
ing. Wisconsin Agr. Exp. Sta., Bui. 230, pp. 7-11. 1913. 



ACID, OR SOUR, SOILS 389 

298. Plants as indicators of acidity. — In addition 
to these chemical tests for acidity there may also be 
mentioned what is perhaps the most reliable indication 
of the need of lime, namely, the failure of a soil to produce 
red clover, and the presence of those weeds that have 
previously been shown to thrive on sour soil (par. 289). 
When a soil bears this relation to the plant growth it may 
safely be assumed that those plants included in the list of 
crops that are injured by sour soils will yield better if the 
soil is limed than if it is not so treated. The crops adapted 
to sour soils may not be injured. 

299. Quantitative determinations of acidity. — A num- 
ber of quantitative methods for determining the degree 
of acidity or the lime requirements of soils have been 
devised. Only a few of these need be mentioned. 

300. Potassium nitrate method.^ — The soil is shaken 
with a normal solution of potassium nitrate for three 
hours, and then allowed to stand overnight. An aliquot 
portion of the supernatant liquid is boiled in order to 
expel carbon dioxide, and when cool it is titrated with 
a standard solution of sodium hydroxide. 

This method does not estimate either the free acid 
or the lime requirement of the soil. What it does is 
to give the absorptive power of the soil for potassium 
when in equilibrium with a solution containing the 
acid with which the potassium was originally in com- 
bination. There is a substitution of bases during the 
contact of the nitrate solution with the soil, and a 
partial decomposition of these salts during the titration 
with alkali. 

» Official and Provisional Methods of Analysis. Association 
of Official Agricultural Chemists. U. S. D. A., Bur. Cham., 
Bui. 107 (revised), p. 20. 1908. 



390 SOILS: PROPERTIES AND MANAGEMENT 

301. Limewater method. — A measured quantity of 
a standard solution of limewater is brought into contact 
with the soil and absorption is accomplished by evapora- 
tion, after which water is added and the filtrate is tested 
with phenolphthalein. Failure to produce a pink color 
shows that the lime requirement of the soil has not been 
reached ; an alkaline reaction shows that an excess of 
lime has been added. A number of tests must be made 
in order to reach a point below which the indicator shows 
no color and above which it does. The lime requirement 
may thus be indicated. This determination was devised 
by Veitch/ and is a useful method since it indicates to 
within a few hundred pounds the quantity of lime re- 
quired to satisfy the absorptive power of a soil. 

302, Resume. — In conclusion, a few facts regarding 
so-called acid soils may be restated : (1) acidity is not 
always due to free acids, but often to the lack of an abun- 
dance of bases ; (2) it is not injurious to all plants, but is 
likely to depress the yields of the majority of agricultu- 
rally important crops, while some valuable ones are bene- 
fited by it; (3) it may be overcome sometimes by aera- 
tion of the soil, and always by the application of lime or 
wood ashes. The correction of acidity by means of lime 
will be discussed in a later chapter, as will also the rela- 
tion of certain bacteria to acidity. 



1 Veitch, F. P. The Estimation of Soil Acidity and the Lime 
Requirements of Soils. Jour. Am. Chem. Soc, Vol. 24, pp. 
1120-1128. 1902. 



CHAPTER XVIII 
ALKALI SALTS 

It has already been shown that soils are acted upon by 
a great variety of weathering agents which gradually 
render soluble a portion of the most susceptible constitu- 
ents. This soluble material becomes a part of the soil 
solution and may come in contact with the roots of any 
crop growing on the soil. In humid regions, w^here a 
large quantity of water percolates through the soil, this 
soluble matter has little opportunity to collect. In arid 
regions, however, where loss by drainage is slight, these 
salts may often collect in large amounts. During periods 
of drought they are carried upward by the capillary rise 
of the soil water, while during periods of rainfall they may 
move downward again in proportion to the leaching action. 
At one time the lower soil may contain considerably more 
soluble salt than the upper ; at another time the condition 
may be reversed, in which case the solution in contact 
w^ith plant roots may contain so much soluble matter 
that vegetation is injured or destroyed. This excess of 
soluble salts usually has a marked alkaline reaction, but 
in any case it produces what is termed an alkali soil. 

303. Composition of alkali salts. — The materials dis- 
solved in the soil water consist of all the substances found 
in the soil, but as the rates of solubility of these substances 
vary greatly there is accunuilated a much larger quantity 
of some substances than of others. Carbonates, sulfates, 

391 



392 SOILS: PROPERTIES AND MANAGEMENT 

and chlorides of sodium, potassium, calcium, and mag- 
nesium occur in the largest amounts. Sodium may be 
present as carbonate, sulfate, chloride, phosphate, and 
nitrate. Potassium may be similarly combined. Mag- 
nesium is likely to appear as a sulfate or a chloride, and 
calcium as a sulfate, a chloride, or a carbonate. One 
salt will predominate in some soils, and other salts in other 
soils. A base may be present in combination with several 
different acids. The nature of the prevailing salt greatly 
influences the effect on vegetation. The table on page 

393 gives the composition of the soluble salts from a 
number of alkali soils. 

A few years ago Headden ^ called attention to large 
accumulations of nitrates in certain localities in Colorado. 
These salts dissolve in the soil water and are frequently 
present in such large quantities as to be injurious to 
vegetation. 

304. White and black alkali. — Sulfates and chlorides 
of the alkalies, when concentrated on the surface of the 
soil, produce a white incrustation, which is very common 
in alkali regions during a dry period as a result of evapora- 
tion of moisture. Incrustations of tlits character are 
called white alkali. 

Carbonates of the alkalies, particularly sodium car- 
bonate, dissolve organic matter from the soil, thus giving 
a dark color to the solution and to the incrustation. For 
this reason alkali containing large quantities of these 
salts is called black alkali. Black or brown alkali may 
also be produced by calcium chloride or by an excess of 
sodium nitrate. 

1 Headden, W. P. Deterioration in the Quality of Sugar 
Beets duo to Nitrates Formed \n the Soil. Colorado Agr. 
Exp. Sta., Bui. 183. 1912. 



ALKALI SALTS 



393 



Percentage Composition of Alkali Salts in Soils 







ox 


ill 

£i D »- 


5." OD 

is 

n < 1 

J*- 


Billings, 
Montana < 


YtJMA, 

Arizona ' 




3 



00 


3 



hH CO 


KCl . 
K2SO4 . 

K.COa 

NaoS04 

NaNOa 

Na^COs 

NaCl . 

Na3HP04 

MgS04 

MgCU . 

CaCl. . 

NaHCOs 

CaS04 

Ca(HC03) 

Mg(HC03 

(NIl4)2CO 


2 . 

)2 . 


1.64 

33.07 
6.61 

12.71 
17.29 

21.48 


3.95 

25.28 
19.78 
32.58 
14.75 
2.25 

1.41 


5.61 
9.73 

13.86 

36.72 

1.87 

16.48 

15.73 


1.60 

85.57 

0.55 
8.90 

0.67 
2.71 


21.41 
35.12 

7.28 

4.06 

22.06 
10.07 


4.00 

81.15 

7.71 
0.25 
0.28 
6.61 


22.10 

13.77 

6.88 
3.98 

21.02 
32.25 



1 Headden, W. P. The Fixation of Nitrogen. Colorado 
Agr. Exp. Sta., Bui. 155, p. 10. 1910. 

2 Hilgard, E. W. Soils, p. 442. New York, 1906. 

' Dorsey, C. W. Alkali Soils of the United States. U. S. 
D. A., Bur. Soils, Bui. 35, p. 79. 1906. 
* Ibid., p. 103. ^ Ibid., p. 109. 



394 SOILS: PROPERTIES AND MANAGEMENT 

Black alkali is much more destructive to vegetation 
than is white. A quantity of white alkali that would 
not seriously interfere with the growth of most crops 
might completely prevent the development of useful 
plants if the alkali were black. 

305. Effect of alkali on crops. — The presence of 
relati\'ely large amounts of salts dissolved in water and 
brought into contact with a plant cell has been shown to 
cause a shrinkage of the protoplasmic lining of the cell, 
the shrinking increasing with the concentration of the 
solution. This causes the plant to wilt, to cease growth, 
and finally to die. The nature of the salt, and the species 
and even the indi\idualit>' of the plant, determine the 
point of concentration at which the plant succumbs. 

The directly injurious effect of the chlorides, sulfates, 
nitrates, and other salts of the alkalies and alkali earths 
is due to this action on the cell contents of the plants. 
The carbonates of the alkalies have, in addition, a cor- 
roding effect on the plant tissues, dissolving the parts 
of the plant with which they come in contact. Indirectly 
alkali salts may injure plants by their influence on the 
soil tilth, soil organisms, and fimgous and bacterial 
diseases. 

306. Effect on different plants. — The factors that 
determine the tolerance of ])lants toward alkali arc : 
(1) the physiological constitution of the plant; (2) the 
rooting habit. The first is not well understood, but 
resistance varies with species, and even with indixiduals 
of the same species. So far as the rooting habit influences 
tolerance of alkali, the advantage is with the (lcoi)-r()()tc(l 
plants such as alfalfa and sugar beets, i)r()bal)ly because 
a part of the root is in a less strongly impregnated part 
of the soil. 



ALKALI SALTS 



395 



Of the cereals, barley and oats are the most tolerant, 
these being able in some cases to produce good crops on 
soil containing two-tenths per cent of white alkali. Of the 
forage crops, a number of valuable grasses are able to 
grow on soil containing considerably more than two-tenths 
per cent of alkali. Timothy, smooth brome, and alfalfa 
are the cultivated forage plants most tolerant of alkali, 
although they do not equal the native grasses in this 
respect. Cotton also tolerates a considerable amount of 
alkali. 

Lough ridge,^ after experiments and observation for a 
number of years, has obtained data regarding the resist- 
ance of various crops to the several alkali salts. His 
results are given in part below, expressed in pounds to 
an acre to a depth of four feet : — 



Crop 


NasSOi 


NazCOa 


,NaCl 


Total Alkali 


Grapes . . . 


40,800 


7,550 


9,640 


45,760 


Oranges . . . 


18,600 


3,840 


3,360 


21,840 


Pears . . . 


17,800 


1,760 


1,360 


20,920 


Apples . . . 


14,240 


640 


1,240 


16,120 


Peaches . . . 


9,600 


680 


1,000 


11,280 


Rye .... 


9,800 


960 


1,720 


12,480 


Barley . . . 


12,020 


12,170 


5,100 


25,520 


Sugar beets 


52,640 


4,000 


5,440 


59,840 


Sorghum 


61,840 


9,840 


9,680 


81,360 


Alfalfa . . . 


102,480 


2,360 


5,760 


110,320 


Saltbush . . 


125,640 


18,560 


12,520 


156,720 



' Loughridge, R. H. Toleranoe of Alkali by Various Cul- 
tures. California Agr. Exp. Sta., Bui. 133. 1901. See also 
Kearney, T. H., and Harter, L. L. Comparative Tolerance of 
Various Plants for the Salts Common in Alkali Soils. U. S. D. A., 
Bur. Plant Indus., Bui. 113. 1907. 



396 SOILS: PROPERTIES AND MANAGEMENT 



Although in general the results as to the resistance to 
alkali of the various crops are so conflicting, the Bureau 
of Soils/ in its alkali mapping, has been able to make a 
rough classification as follows : — 



Percentage op Total 


Percentage op 


Chops 


Salts 


Black Alkali 


to 0.20 


Less than 0.05 


All crops grow 


0.20 to 0.40 


0.05 to 0.10 


All but most sensitive 


0.40 to 0.60 


0.10 to 0.20 


Old alfalfa, sugar beet, 
barley, and sorghum 


0.60 to 1.00 


0.20 to 0.30 


Only most resistant plants 


1.00 to 3.00 


0.30 and above 


No plants 



307. Other conditions that influence the action of 
alkali. — The higher the water content of the soil, the 
less is the injury to plants from alkali ; but should 
the same soil become dry, the previous large quantity of 
water would, by bringing into solution a larger amount 
of alkali, render the solution stronger than it would 
otherwise have been, and thus cause greater injury (see 
Fig. 57). 

The distribution of the alkali at diiVerent depths may 
have an important bearing on its effect on plants. 
Young plants and shallow-rooted crops may be entirely 
destroyed by the concentration of alkali at the surface, 
while the same quantity evenly distributed through the 
soil, or carried by moisture to a lower depth, would have 
caused no injury. A loam soil, by reason of its greater 
water-holding capacity and adsorptive power, will carry 
more alkali without injury to plants than will a sandy 



1 Dorsey, C. W. Alkali Soils of the United States. 
D. A., Bur. Soils, Bui. 35, pp. 23-25. 1906. 



U. S. 



ALKALI SALTS 



397 



soil. Certain of the alkali salts exert a deflocculating 
action on clay soils and effect an indirect injury in that 
wav. 





^Mounrs or 


IS 3 


100 OF JOIL 


n J.^ SB SS 




I 














































k 

^ 


V- 


~^^^;^ 


^^ 




















( \ 




"; 
/ 

L^ 


















' V 


~^^^' 






''~~~~Sc 






-^^"■^i ' _ 


sa^22___ 






^ 

§ 
J 


,^t^o^ 


y 








-/UJ(/IU H. 


tllO(i4H- 




^j> 




> 


r 


r 


-^ 


■J^^^-^ 


'■^ 














-* 




^J^ 





















Fig. 57. — Diagram showing the amount and composition of alkali salts 
at various depths. Tulare, California. 



308. Accumulation of alkali. — The alkali salts, being 
readily soluble, are carried by the soil water where there 
is any lateral movement, as is often the case where land 
slopes to some one point. Low-lying lands adjacent to 
such slopes are thus likely to contain considerable alkali, 
and the " alkali spots " of semiarid regions and the 
large accumulations of alkali in many of the valley lands 
of arid regions are traceable to this cause. 

309. Irrigation and alkali. — In irrigated regions, the 
injurious ellect of alkali is in many cases discovered only 



398 SOILS: PROPERTIES AND MANAGEMENT 

after irrigation has been practiced for a few years. This 
is due to what is known as a " rise of alkaH," and comes 
about through the accumulation, near the surface of the 
soil, of salts that were formerly distributed throughout 
a depth of perhaps many feet. Before the land was 
irrigated, the rainfall penetrated only a slight depth into 
the soil, and when evaporation took place, salts were 
drawn to the surface from only a small volume of soil. 
When, however, irrigation water is turned on the land, 
the soil becomes wet to a depth of perhaps fifteen or 
twenty feet. During the portion of the year in which 
the soil is allowed to dry, large quantities of salts are 
carried toward the surface by the upward-moving capil- 
lary water. Although these salts are in part carried 
down again by the next irrigation, the upward movement 
constantly exceeds the downward one. This is because 
the descending water passes largely through the non- 
capillary interstitial spaces, while the ascending water 
passes entirely through the capillary spaces. The smaller 
spaces, therefore, contain a considerable quantity of 
soluble salts after the downward mo\ement ceases and 
the upward movement begins. In other words, the 
volume of water carrying the salts downward in the 
capillary spaces is less than that carrying them upward 
through these spaces. Surface tension causes the salts 
to accumulate largely in the capillary spaces, and it is 
therefore the direction of the principal movement through 
these spaces that determines the point of accumulation 
of the alkali. 

There are large areas of land in Egypt, in India, and 
even in France and Italy, as well as in this country, that 
have suffered in this way, and not infrequently they have 
reverted to a desert state. 



ALKALI SALTS 399 

310. The handling of alkali lands. ^ — Ordinarily there 
are two general ways in which alkali lands may be handled 
in order to avoid the injurious effect of soluble salts. 
The first of these is eradication, the second may be 
designated as control. In the former case, an at- 
tempt is made to actually eliminate by various means 
some of the alkali. In the latter, methods of soil 
management are employed which will keep the salts 
well distributed throughout the soil. In many cases 
soils would grow excellent crops if the alkali could 
only be kept well distributed through the soil layers 
so that no toxic action could occur, at least within 
the root zone. In general, steps should always be taken 
toward the control of alkali, whether eradication is at- 
tempted or not. Under irrigation, careful control is 
always wise. 

311. Eradication of alkali. — Of methods designed to 
at least partially free the soil of alkali, the commonest 
are : (1) leaching with underdrainage, (2) correction with 
gypsum, (3) scraping, and (4) flushing. 

312. Leaching with underdrainage. — Of the various 
methods for removing an excess of soluble salts, the use 
of tile drains is the most thorough and satisfactory. 
When this method is used in an irrigated region, heavy 
and repeated applications of water must be made, to 
leach out the alkali from the soil and drain it off through 
the tile. When used for the amelioration of alkali spots 

1 Dorsey, C. W. Reclamation of Alkali Soils. U. S. D. A., 
Bur. Soils, Bui. 34. 1906. Also, Hilgard, E. W. Utilization 
and Reclamation of Alkali Lands, Soils. New York, 1911. 
Also, Brown, C. F., and Hart, R. A. Reclamation of Seeped 
and Alkali Lands. Utah Agr. Exp. Sta., Bui. 111. 1910. 
Also, Dorsey, C. W. Reclamation of Alkali Soils at BiUings, 
Montana. U. S. D. A., Bur. Soils, Bui. 44. 1907. 



400 SOILS: PROPERTIES AND MANAGEMENT 

in a semiarid region, the natural rainfall will in time 
effect the removal. 

In laying tiles it is necessary to have them at such a 
depth that soluble salt in the soil beneath them will not 
readily rise to the surface. This will depend on those 
properties of the soil governing the capillary move- 
ment of water. Three or four feet in depth is usually 
sufficient, but the capillary movement should first be 
estimated. 

After the drains have been placed, the land is flooded 
with water to a depth of several inches. The water is 
allowed to soak into the soil and to pass oft' through the 
drains, leaching out part of the alkali in the process. 
Before the soil has time to become very dry the flooding 
is repeated, and the operation is kept up until the land 
is brought into a satisfactory condition. 

Crops that will stand flooding may be grown during 
this treatment, and they will serve to keep the soil 
from puddling, as it is likely to do if allowed to become 
dry on the surface. If crops are not grown, the soil 
should be harrowed between floodings. The operation 
should not be carried to a point where the soluble 
salts are reduced below the needs of the crop, or so 
low that they lose entirely their effect on the retention 
of moisture. 

313. Correction with gypsum. — The use of gypsum 
on black alkali land has sometimes been practiced for 
the purpose of converting the alkali carbonates into 
sulfates, thus ameliorating the injurious properties of 
the alkali without decreasing the amount. The quantity 
of gypsum required may be calculated from the amount 
and composition of the alkali. The soil must be kept 
moist, in order to bring about the reaction, and the 



ALKALI SALTS 401 

gypsum should be harrowed into the surface, not plowed 
under. The reaction is as follows : — 

NaaCOs + CaS04 = CaCOs + Na2S04 

When soil containing black alkali is to be tile-drained, 
it is recommended that the land shall first be treated 
with gypsum, as the substitution of alkali sulfates for 
carbonates causes the soil to assume a much less compact 
condition and thus facilitates drainage. It also prevents 
the loss of organic matter dissolved by the carbonate of 
soda and the soluble phosphates, both of which are pre- 
cipitated by the change. 

314. Scraping. — Removal of the alkali incrustation 
that has accumulated at the surface is sometimes re- 
sorted to. Very often the rise of alkali is encouraged 
by applications of irrigation water, w^hich is allowed 
to evaporate unretarded. The salts are thus carried 
upward by the capillary movement of the soil water. 
This method of alkali eradication is never very effi- 
cient, and is often dangerous, as it encourages the 
presence of very large amounts of alkali salts in the sur- 
face soil. 

315. Flushing. — Often alkali accumulations may be 
washed from the soil surface by turning on a rapidly 
moving stream of water. The texture of the soil, as well 
as the slope of the land, must be just right for such a 
procedure. Generally so much water enters the soil 
that the land remains heavily impregnated with alkali 
salts. Both this method and the previous one, even 
if successful, are only temporary. Moreover, lands 
carrying so much alkali as to admit of either one of these 
procedures may be so heavily charged as never to yield 
to anv form of either eradication or control. 



402 SOILS: PROPERTIES AND MANAGEMENT 

316. Control of alkali. — Where excessive amounts of 
soluble salts do not exist in a soil, the control of the alkali 
with a view of keeping it well distributed in the soil 
column is the best practice. The retardation of evapora- 
tion is, of course, the main object in this procedure. The 
intensive use of the soil mulch is therefore to be advocated, 
especially in all irrigation operations where alkali concen- 
trations are likely to occur. Such a method of soil 
management not only saves moisture, but also prevents 
the excessive translocation of soluble salts into the root 
zone. This method of control is the most economical, 
the cheapest, and the one to be advocated on all occasions, 
no matter what may have been the previous means of 
dealing with the alkali situation. 

317. Cropping with tolerant plants. — Certain soils 
that are strongly impregnated with alkali may be grad- 
ually improved by cropi)ing with sugar beets and other 
crops that are tolerant of alkali and that remove large 
quantities of salts. This is more likely to be efficacious 
where irrigation is not practiced. Certain crops, more- 
over, while somewhat seriously injured while young, are 
very resistant once their root systems are developed. 
A good example is alfalfa, the young plants being ^•ery 
tender while the more mature ones are extremely resistant. 
Temporary eradication of alkali may allow such a crop to 
be established. It will then maintain itself in spite of the 
concentrations that may later occur. 

318. Alkali spots. — In semiarid regions small areas of 
alkali are often found, varying from a few square yards 
to several acres in size. The quantities of alkali in these 
are usually not sufficient to prevent the growth of plants 
in years of good rainfall, but in periods of drought the 
concentration of the salts and the compact condition that 



ALKALI SALTS 403 

they tend to produce combine to injure the crop. The 
methods already mentioned for treating alkali land are 
of service on these small areas, and, in addition, the 
plowing-under of fresh farm manure has been found to 
improve their productiveness. This, with surface drain- 
age, deep tillage, and good cultivation in order to prevent 
the soil from drying out, will usually remedy the difficulty. 
In many cases these spots become highly productive under 
proper treatment. 



CHAPTER XIX 

ABSORPTION OF NUTRITIVE SALTS BY 
AGRICULTURAL PLANTS 

All the salts taken up by the roots of agricultural 
plants are in solution when absorbed. The movement 
into the root thus depends on the presence of moisture, 
which is the medium of transfer. The root-hairs are the 
great absorbing organs of the plant, and through the 
cells of their delicate tissues the solutions of the various 
salts are passed. 

319. How plants absorb nutrients. — The nature and 
quantity of material absorbed by a plant is determined 
by the law of osmosis. From the cells of the root-hairs 
the dissolved salts are transferred to other parts of the 
plant, where they imdergo the metabolic processes that 
determine which constituents shall be retained in the 
tissues of the plant. The unused ions that remain in 
the plant juices prevent by their presence the further 
absorption of those particular substances from the soil 
water. It thus happens that the composition of the 
ash of a plant may be very different from that of the 
substances presented to it in solution. For example, 
aluminium, although always present in the soil in a very 
slightly soluble form, is present in mere traces in the ash 
of most plants. On the other hand, iodine, although 
present in sea water only in the most minute quantities, 
is present in large quantities in the ash of certain marine 
alga?. 

404 



ABSOnPTlON OF NUTRITIVE SALTS 405 

A plant will, in general, take up more of a nutritive 
substance if it is presented in large amount, as compared 
with the other soluble substances in the nutrient solution, 
than if it is presented in small amount. Thus, the per- 
centage of nitrogen in maize, oats, and wheat may be 
increased by increasing the ratio of nitrogen to other 
nutritive substances in the nutrient media. This is 
also true of potassium and phosphorus, respectively. 
This fact is accounted for by the maintenance of the 
osmotic equilibrium at a higher level for a particular 
ion which is relatively abundant in the nutrient solution, 
thus preventing the return of the excess from the plant. 

320. Relation between root-hairs and soil particles. — 
In a rich, moist soil the number of root-hairs is very 
great, while in a poor or a very dry soil or in a saturated 
soil there are comparatively few root-hairs. The con- 
nection between the root-hairs and the soil particles is 
extremely intimate. When in contact with a particle 
of soil, a root-hair in many cases almost incloses it, and 
by means of its mucilaginous wall forms a contact so close 
as practically to make the solution between the particle 
and the cell wall distinct from that between the soil 
particles themselves. 

There has been considerable difference of opinion as to 
how a plant can obtain its mineral nutrients from a sub- 
stance so difficultly soluble as the soil. This has arisen 
because of the conflicting nature and the inadequate 
character of the data available. 

321. Liebig and Sachs on solvent action of plant 
roots. — Liebig ' called attention to the fact that a plant 
may obtain one hundred times as much phosphorus and 

1 Liebig, J. Die Chemie in Ilu-er Anwendung auf Agrikultur. 
1862. 



406 SOILS: PROPERTIES AND MANAGEMENT 

nitrogen and fifty times as much potassium as can be 
extracted from the same vohmie of soil with pure water 
or with water containing carbon dioxide. It has, of 
course, been recognized that the soil water is aided in its 
solvent action by a variety of substances that may be 
normally present in solution, beginning with the gases 
taken up by rain in its descent through the atmosphere, 
and further added to by the carbon dioxide and the or- 
ganic and mineral substances obtained from the soil. It 
has been held that the plant roots aid solution of mineral 
matter by excretion of acids, which act effectively as 
solvents. The well-known root tracings on limestone 
and marble have been taken as proof of the excretion of 
such acids. Sachs, ^ and later other investigators, grew 
plants of various kinds in soil and other media in which 
was placed a slab of polished marble or dolomite or cal- 
cium phosphate, covered with a layer of washed sand. 
After the plants had made sufficient growth the slabs were 
removed, and on the surfaces were found corroded trac- 
ings, corresponding to the lines of contact between the 
rootlets and the minerals. 

322. Czapek's experiments. — In order to test this 
theory, Czapek - repeated the experiments of Sachs, 
using plates of gypsum mixed with the ground mineral 
that he wished to test, and this mixture he spread over a 
glass plate. Using these plates in the same manner as 
previously described, Czapek found that, while plates of 
calcium carbonate and of calcium phosphate were cor- 
roded by the plant roots, plates of aluminium phosphate 

* Sachs, J. Auflosung des Marmors durch Mais-Wurzeln 
Bot. Zeitung, 18 Jahrgang, Seite 117-119. 1860. 

"^ Czapek, J. Zur Lehre von den Wurzelausscheidung. Jahrb. 
f. Wiss. Bot., Band 29, Seite 321-390. 1896. 



ABSORPTION OF NUTRITIVE SALTS 407 

were not. He concludes that if the tracings are due to 
acids excreted by the plant roots, the acids so excreted 
must be those that have no solvent action on aluminium 
phosphate. This would limit the excreted acids to car- 
bonic, acetic, propionic, and butyric. Czapek also re- 
plies to the argument that the acids producing the tracings 
must be non-volatile ones because of the definite lines 
made in the mineral, by stating that the excretion of 
carbon dioxide alone would be sufficient to account for 
the observations since it dissolves in water to form car- 
bonic acid, and that carbonic acid is always present in 
the cell walls of the root epidermis. By means of micro- 
chemical analyses of the exudation's of root-hairs grown 
in a water-saturated atmosphere, Czapek found potassium, 
magnesium, calcium, phosphorus, and chlorine in the 
exudate. He concludes that the solvent action of plant 
roots is due to acid salts of mineral acids, particularly 
acid potassium phosphate. He has not proved, however, 
that the exudations were not from dead root-hairs nor 
from the dead cells of the rootcap. In either case they 
would have some solvent action, but whether sufficient 
to make them of importance is doubtful. 

323. Secretion of an oxidizing enzyme by plant roots. — 
Molisch ^ found that root-hairs secrete a substance having 
properties corresponding to those of an oxidizing enzyme. 
His work has been repeated by others who have failed to 
obtain similar results, but lately Schreiner and Reed ^ have 

1 Moliseh, H. Ueber Wurzelausseheidungen und deren 
Ein\Nirkung auf Organische Substanzen. Sitzungsber. Akad. 
Wiss. Wien-Math. Nat., Band 96, Seite 84-109. 1888. Ab- 
stract in Chem. Centrlb., Band 18, Seite 1513. 1888, and in 
Centrlb. f. Agr. Chem., Band 17, Seite 428, 1888. 

- Schreiner, Oswald, and Reed, H. S. Studies on the Oxidiz- 
ing Powers of Roots. Bot. Gazette, Vol. 47, p. 355. 1909. 



408 SOILS: PROPERTIES AND MANAGEMENT 

demonstrated an oxidizing action of roots that is appar- 
ently due to a peroxidase. Oxidation alone, however, 
would hardly suffice to account for the solvent action 
accompanying the development of plant roots, although 
it is doubtless an important function and useful in other 
ways. 

324. Importance of carbon dioxide as a solvent. — 
Stoklasa and Ernst ^ have contributed much to this sub- 
ject during the last decade. Stoklasa's earlier experiments, 
conducted by maintaining the plant roots in a saturated 
atmosphere, gave only carbon dioxide in the exudate. 
In this he is in agreement with most of the recent inves- 
tigators of this subject. Stoklasa emphasizes the im- 
portance of carbon dioxide as a solvent by showing the 
quantity produced by plants and by microorganisms. 
He estimates that in one acre of soil to a depth of sixteen 
inches there are sixty-eight pounds of carbon dioxide 
produced by bacterial respiration in two hundred days, 
and fifty-four pounds of carbon dioxide excreted by plant 
roots in one hundred days; these periods he considers 
as representing the year's activity of bacteria and higher 
plants. 

In later experiments, Stoklasa and Ernst - found that 
when plants do not have a sufficient supply of oxygen in 
the air surrounding their roots, they secrete acetic and 
formic acids from the root-hairs. These investigators 
believe that these acids are toxic rather than beneficial. 



1 Stoklasa, J., and Ernst, A. Ueber den Ursprung die Menge 
und die Bcdeutung dcs Kohlendioxyds iin Boden. Centrlb. f. 
Bakt., II, Band 14, Seite 723-736. "l9()5. 

2 Stoklasa, J., and Ernst, A. Beitnige zur Losung der Frage 
der Chemischen Natur des Wurzelsekretes. Jahrb. f. Wiss. 
Bot., Band 40, Soite 55-102. 1908-1909. 



ABSORPTION OF NUTRITIVE SALTS 409 

and that they are responsible, in large measure, for the 
injurious effect on plants of a very compact condition of 
soil. In the same communication these authors report 
an experiment in which it was found that the kinds of 
plants that excrete the largest quantity of carbon dioxide 
from their roots are the ones that absorb the greatest 
quantities of phosphorus from gneiss and from basalt. 
This, however, does not necessarily connote any conse- 
quential relation between these physiological functions. 

Barakov ^ drew air through planted soils contained in 
large tanks. He found that the maximum production 
of carbon dioxide occurred at the time when the plants 
were blossoming, whether the plants blossomed early 
or late in the season. This he considered to indicate 
that the plant assists most" vigorously in the solution of 
nutrient materials at the time when it is most active in 
absorbing them. 

325. Insufficiency of carbon dioxide. — Pfeiffer and 
Blanck - passed carbon dioxide through soil contained in 
vessels in which plants were growing. The soil in some ves- 
sels contained a difficultly soluble tricalcic phosphate, that 
in other vessels the more easily soluble dicalcic phosphate, 
and that in still other vessels was unfertilized. Another 
set of vessels having the same fertilizer treatment received 
no carbon dioxide. The soil receiving carbon dioxide 
produced larger yields of dry matter and phosphorus in 

' Barakov, F. The Carbon Dioxide Content of Soils at 
Different Periods of Plant Growth. Jour. Exp. Agr. (Russian), 
Vol. 11, pp. 321-342. 1910. The authors are indebted to 
Dr. J. Davidson for a translation of this paper. 

2 Pfeiffer, Th., and Blanck, E. Die Saureausseheidung 
der Wurzeln und die Losliehkeit der Bodennahrstoffe in Koh- 
lensaurehaltigem Wasser. Landw. Vers. Stat., Band 77, Seite 
217-268. 1912. 



410 SOILS: PROPERTIES AND MANAGEMENT 

the crop on the soil to which dicalcic phosphate had been 
appHed than did the soil not receiving carbon dioxide ; 
but the soil to which no phosphate was added yielded 
equally well whether it received carbon dioxide or not. 
The plants used were oats, peas, and lupines. These 
investigators conclude that carbon dioxide is not a suffi- 
cient solvent to account for the mineral nutrients obtained 
from soils by plants. 

326. The present status of the question. — The avail- 
able evidence on excretion of acids other than carbonic 
by the roots of plants does not admit of any very satis- 
factory conclusion as to their relative importance in the 
acquisition of plant-food materials. There can be no 
doubt, however, that carbon dioxide resulting from root 
exudation and from decomposition of organic matter in 
the soil plays a very prominent part in this operation. 
The very large quantity of carbon dioxide in the soil, 
amounting in some cases to from .5 to nearlj- 10 per cent 
of the soil air, or several hundred times that of the at- 
mospheric air, must aid greatly in dissolving the soil 
particles. 

Whatever may be the concentration of the soil water, 
it seems probable that the liquid which is found where 
the root-hair comes in contact with the soil particle, and 
which is separated, in part at least, from the remainder 
of the soil water, must have a density much greater than 
that found elsewhere in the soil. That portion of the 
soil water immediately in contact with the soil grain is a 
much stronger solution than the water farther from the 
soil surfaces, because of the adsorptive action of the 
particles. 

Many plants grown in solutions of nutritive salts have 
few or no root-hairs, but absorb through the epidermal 



ABSORPTION OF NUTRITIVE SALTS 411 

tissue of the roots. If the plant depended wholly on the 
prepared solution in the soil water, a similar structure 
would doubtless suffice. The special modification by 
which the root-hairs come in intimate contact with the 
soil particle and almost surround it, indicates a direct 
relation between the soil particles and the plant, and 
not merely between the soil solution and the plant. 

New root-hairs are constantly being formed, and the 
old ones become inactive and disappear. The contact 
of a root-hair with a soil particle is not long-continued. 
Whether the period of contact is determined by the 
ability of the root to absorb nutriment from the particle 
is not known. Certain it is that only a small portion of 
the particle is removed. 

327. Possible root action on colloidal complexes. — 
It has already been stated that there is some evidence 
to lead to the belief that the surfaces of soil particles are 
covered to a large extent with colloidal complexes, com- 
posed of both organic and inorganic matter having vigor- 
ous absorptive properties and holding the bases and phos- 
phorus in an absorbed condition. Roots of growing 
plants have been found to cause coagulation of at least 
some colloids, possibly by leaving an acid residue in the 
nutrient solution by reason of the selective absorption of 
bases and rejection of the acids of the dissolved salts. 
It is conceivable that the root-hair, by removing bases 
from the solution existing between the cell wall and the 
colloidal covering of the soil particle, may cause coagula- 
tion of the colloidal matter and thus liberate the plant- 
food materials held by absorption. The liberated ma- 
terial, being of a readily soluble nature, would be taken 
up by the solution between the rootlet and the soil particle, 
from which the root-hair could readily absorb it. Such 



412 SOILS: PROPERTIES AND MANAGEMENT 

an liypothesis would account for the ability of plants 
to obtain a quantity of nutrient materials far in excess of 
what can be accounted for by the solvent action of pure 
water, and even beyond what many investigators are 
willing to attribute to the solvent action of water charged 
with carbon dioxide. 

328. Why crops vary in their absorptive powers. — 
As has already been pointed out (pars. 3ol-.'^;^()), crops of 
different kinds vary greatly in their ability to draw 
nourishment from the soil. The difl'erence between the 
nitrogen, phosphorus, and potassium taken up by a corn 
crop of average size and a wheat crop of average size is 
very striking. In the ta})le on page 419 it is seen that 
two tons of red clover contain three times as much potash, 
nearly ten times as much lime, and somewhat more phos- 
phoric acid than does a crop of thirty bushels of wheat 
including the straw. 

The difference in absorbing power may be due to either 
one or both of two causes : (1) a larger absorbing system ; 
(2) a more acti\'e absorbing system. The former is deter- 
mined by the extent of the root-hair surfaces; the latter 
by the intensity of the osmotic action. 

329. Extent of absorbing system. — Plants with large 
root systems may be expected to absorb the larger amounts 
of nutrients from the soil. Such is usually the case, 
although the extent of the root system is not necessarily 
proportional to the total area of the absorbing surfaces 
of the root-hairs. 

330. Osmotic activity. — The osmotic activity of a 
plant under any given condition of soil and climate de- 
pends on: (1) the rapidity and completeness with which 
the plant elaborates the substances taken from the soil 
into plant substance, or otherwise removes them from 



ABSORPTION OF NUTRITIVE SALTS 413 

solution ; (2) the extent to which the exudations from the 
root-hairs — whether these be carbon dioxide, salts of 
mineral acids, or organic acids — act on the soil particles. 

The first of these is a function of the vital energy of the 
plant and its ability to utilize sunshine and carbon dioxide 
to produce organic matter. It may be compared to the 
property which enables one animal to do more w^ork than 
another animal of the same weight on a similar ration. 

The removal from the ascending water current in the 
plant of substances derived from the soil is accomplished 
in the leaves. By the dissociation of these substances, 
ions are constantly furnished for metabolism into materials 
that may be built into the tissues of the plant. The re- 
maining ions are kept in the solution. There is a con- 
stant tendency to bring the composition and density of 
the solution into equilibrium, by diffusion and diosmosis, 
with the solution between the soil particle and the root- 
hair. The rapidity with which the metabolic process 
removes a substance from the solution in the plant, there- 
fore, determines the rate at which it is removed from a 
solution of given composition and density in the soil. 
Plants making a rapid growth remove more nutrients in 
a given time than those making a slower growth, when 
the nutrient solution is of a given composition and density. 

Another factor that affects the rate of absorption of 
salts from the soil is the solvent influence of exudates from 
the root-hairs. This subject has already been treated (pars. 
321-326), and it only remains to be said that this action 
apparently varies with different kinds of plants, and 
probably accounts in no small measure for the difference 
in the ability of different plants to withdraw salts from 
the soil. 

These several factors, which, Avhen combined, deter- 



414 SOILS: PROPERTIES AND MANAGEMENT 

mine the so-called " feeding power " of the plant, are 
recognized by the popular terms " weak feeder " and 
" strong feeder," — applied, on the one hand, to such 
crops as wheat or onions, which require very careful soil 
preparation and manuring, and, on the other hand, to 
maize, oats, or cabbage, which demand relatively less 
care. In the manuring and rotating of crops, this differ- 
ence in absorptive power must be considered, in order not 
only to secure the maximum effect on the crop manured, 
but also to get the greatest residual effect of the manure 
on succeeding crops. 

331. The absorptive power of cereals. — Cereals have 
the power of utilizing the potassium and phosphorus of 
the soil to a considerable degree, but they generally re- 
quire fertilization with nitrogen salts. Most of the cereals, 
such as wheat, rye, oats, and barley, take up the principal 
part of their nitrogen early in the season, before the nitri- 
fication processes have been sufficiently operative to fur- 
nish a large supply of nitrogen ; hence nitrogen is the 
fertilizer constituent that usually gives the best results, 
and should be added in a soluble form. Wheat, in partic- 
ular, needs a large amount of soluble nitrogen early in 
its spring growth. Since it is a " delicate feeder," it does 
best after a cultivated crop or a fallow, by which the 
nitrogen has been converted into a soluble form. Oats 
can make better use of the soil fertility and do not require 
so much manuring. Maize is a very coarse " feeder," 
and, while it removes a large quantity of plant-food from 
the soil, it does not require that this shall be added in a 
soluble form. Farm manure and other slowly acting 
manures may well be appliefl for the maize crop. The 
long growing period required by the maize plant gives it 
opportunity to utilize the nitrogen as it becomes avail- 



ABSORPTION OF NUTRITIVE SALTS 415 

able during the summer, when ammonification and nitri- 
fication are active. Phosphorus is the substance usually 
most needed by maize. 

332. The feeding of grass crops. — Grasses, when in 
meadow or in pasture, are greatly benefited by manures. 
They are less vigorous " feeders " than the cereals, have 
shorter roots, and, when left down for more than one 
year, the lack of aeration in the soil causes decomposition 
to decrease. There is usually a more active fixation of 
nitrogen in grass lands than in cultivated lands, but this 
becomes available very slowly. 

Dift'erent soils and different climatic conditions neces- 
sitate different methods of manuring for grass. Farm 
manures may well be applied to meadows in all situations, 
while the use of nitrogen is generally profitable. 

333. Leguminous crops. — Most of the leguminous 
crops are deep-rooted and are vigorous " feeders." Their 
ability to take nitrogen from the air makes the use of that 
fertilizer constituent unnecessary except in a few in- 
stances, such as young alfalfa on poor soil, where a small 
application of nitrate of soda is usually beneficial. Lime 
and potassium are the substances most beneficial to leg- 
umes on the majority of soils. 

334. Root crops. — Many root crops will utilize very 
large quantities of plant-food if it is in a form in which 
they can use it. Phosphates and nitrogen are the sub- 
stances generally required, the latter especially by beets 
and carrots. 

335. Vegetables. — In growing vegetables, the object 
is to produce a rapid growth of leaves and stalks rather 
than seeds, and often this growth is made very early in 
the season. As a consequence, a soluble form of nitrogen 
is very desirable. Farm manure should also have a promi- 



416 SOILS: PROPERTIES AND MANAGEMENT 

nent part in the treatment, as it keeps the soil in a mechan- 
ical condition favorable to retention of moisture, which 
vegetables require in large amounts, and it also supplies 
needed fertility. The very intensive method of culture 
employed in the production of vegetables necessitates the 
use of much greater quantities of manures than are used 
for field crops, and the great value of the product justifies 
the practice. 

336. Fruits. — In manuring fruits, with the exception 
of some of the small, rapidly-growing ones, it is the aim 
to maintain a continuous supply of nutrients available 
to the plant, but not sufficient for stimulation except 
during the early life of the tree, when rapid growth of 
wood is desired. An acre of apple trees in bearing re- 
moves as much plant-food material from the soil in a 
season as does an acre of wheat. Farm manure and a 
complete fertilizer may be used, of which the constituents 
should be in a fairly available form, as a constant supply 
is necessary. A young growing orchard requires con- 
siderably more nitrogen than does an old orchard. Some 
nitrate of soda in early spring is desirable. 

337. Mineral substances absorbed by plants. — The 
plant, in its process of growth, withdraws from the soil 
certain mineral substances that are presented to its roots 
in a dissolved condition. As the salts in solution are 
rather numerous, and as the osmotic pressure by which 
the absorption is accomplished does not admit of the entire 
exclusion of any ion capable of diosmosis, there are to be 
found in the plant most of the mineral constituents of the 
soil. Some of these are concerned in the vital processes 
of the plant and are essential to its growth ; others seem 
to have no specific function, but are generally present. 

The substances commonly met with in the ash of plants 



ABSORPTION OF NUTRITIVE SALTS 417 

are potassium, sodium, calcium, magnesium, iron, man- 
ganese, aluminium, phosphorus, sulfur, silicon, and chlo- 
rine. In addition to these, nitrogen is absorbed from the 
soil in the form of soluble salts. Of these the substances 
known to be absolutely essential to the normal growth of 
plants to maturity, are potassium, calcium, magnesium, 
iron, phosphorus, sulfur, and nitrogen, while the others 
are probably beneficial to the plant in some way not yet 
discovered. 

Of the substances acting as plant nutrients, each must 
be present in an amount sufficient to make possible the 
maximum growth consistent with other conditions, or 
the yield of the crop will be curtailed by its deficiency. 
To some extent certain essential substances may be re- 
placed by others, as, for instance, potassium by sodium ; 
but such substitution is probably possible only in some 
physiological role other than that of an elemental con- 
stituent of an organic compound. The substances that are 
likely to be so deficient in an available form in any soil 
as to curtail the yield of crops, are potassium, phosphorus, 
nitrogen, and possi})ly sulfur ; while the addition of cer- 
tain forms of calcium is likely to be beneficial because of 
its relation to other constituents and properties of the soU. 
It is for the purpose of supplying these substances, and 
to some extent to improve the mechanical condition of 
the soil, that mineral manures are used. 

338. Relation of plant growth to concentration of nu- 
trient solution. — It has already been stated that the 
addition of soluble salts to a soil has been found by some 
experimenters to apparently increase the concentration 
of the soil solution (par. 250). It has also been found 
that plant growth, as measured by weight of plants, in- 
creases with the concentration of the nutrient solution in 
2e 



418 soils: properties and management 

whicli the plants are grown. ^ This is the way in which 
it is generally believed that soluble fertilizer salts benefit 
plant growth. Insoluble plant-food materials have a 
similar, but less active, result because they do not increase 
the concentration of the soil solution to as great an extent. 

339. Quantities of plant-food material removed by 
crops. — The utilization of mineral substances by crops 
is a source of loss of fertility to agricultural soils. In a 
state of nature, the loss in this way is comparatively small, 
as the native vegetation falls on the ground, and in the 
process of decomposition the ash is almost entirely returned 
to the soil. Under natural conditions, soil usually in- 
creases in fertility ; for, while there is some loss through 
drainage and other sources, this is more than counter- 
balanced by the action of the natural agencies of disin- 
tegration and decomposition, and the fixation of atmos- 
pheric nitrogen affords a constant, though small, supply 
of that important soil ingredient. 

When land is put under cultivation, a very different 
condition is presented. Crops are removed from the 
land, and only partially returned to it in manure or straw. 
This withdraws annually a certain small proportion of 
the total quantity of mineral substances, but, what is of 
more immediate hnportance, it withdraws all of this in a 
readily available form. 

The following table, computed by Warington, - shows 

1 Hall, A. D., Brenchley, W. E., and Underwood, L. M. 
The Soil Solution and the Mineral Constituents of the Soil. 
Philosoph. Trans. Royal Soe. London, Series B, Vol. 204, pp. 
179-200. 1913. Also, Lyon, T. L., and Bizzell, J. A. The 
Plant as an Indicator of the Relative Density of Soil Solutions. 
Proc. Am. Soe. Agron., Vol. 4, pp. 35-49. 1912. 

2 Warington, R. Chemistry of the Farm, pp. 64-65. Lon- 
don. 1894. 



ABSORPTION OF NUTRITIVE SALTS 



419 



the quantities of nitrogen, potassium, phosphorus, and 
lime removed from an acre of soil by some of the common 
crops. The entire harvested crop is included : — 







Total 


NlTBO- 


Potash 


Lime 


Phos- 
phoric 


Crop 


Yield 


Ash 


N 


K2O 


CaO 


Acid 
P2O6 






(Pounds) 


(Pounds) 


(Pounds) 


(Pounds) 


(Pounds) 


Wheat .... 


30 bushels 


172 


48 


28.8 


9.2 


21.1 


Barley . . 




40 bushels 


157 


48 


35.7 


9.2 


20.7 


Oats . . 




45 bushels 


191 


55 


46.1 


11.6 


19.4 


Maize . . 




30 bushels 


121 


43 


36.3 


— 


18.0 


Meadow hay 




1| tons 


203 


49 


50.9 


32.1 


12.3 


Red clover 




2 tons 


258 


102 


83.4 


90.1 


24.9 


Potatoes 




6 tons 


127 


47 


76.5 


3.4 


21.5 


Turnips 




17 tons 


364 


192 


148.8 


74.0 


33.1 



340. Quantities of plant-food materials contained in 
soils. — Comparing the figures given above with those 
showing the percentages of the fertilizing constituents in 
certain soils, it is evident that there is a supply in most 
arable soils that will afford nutriment for average crops 
for a very long period of time. (See pars. 46, 48, 52, 53.) 

341. Possible exhaustion of mineral nutrients. — On 
the other hand, when it is considered that the soil must 
be depended upon to furnish food for humanity and 
domestic animals as long as they shall continue to in- 
habit the earth, at least so far as is now known, the very 
apparent possibility of exhausting, even in a period of 
several hundred >'ears, the supply of plant nutrients be- 
comes a matter of grave concern. The visible sources of 
supply, to replace or supplement those in the soils now 
cultivated, are, for the mineral substances, the subsoil 
and the natural deposits of phosphates, potash salts, and 



420 SOILS: PROPERTIES AND MANAGEMENT 

limestone ; and for nitrogen, deposits of nitrates, the by- 
product of coal distillation, and the nitrogen of the 
atmosphere. The last of these is inexhaustible, and the 
exliaustion of the nitrogen supply, which a few years ago 
was thought to be a matter of less than half a century, 
has now ceased to cause any apprehension. The conser- 
vation or extension of the supply of mineral nutrients is 
now of supreme importance. The utilization of city refuse 
and the discovery of new mineral deposits are develop- 
ments well within the range of possibility, but neither of 
these promises to afford more than partial relief. The 
utilization of the subsoil through the gradual removal by 
natural agencies of the topsoil will, without doubt, tend 
to constantly renew the supply. The removal of topsoil 
by wind and erosion is, even on level land, a very con- 
siderable factor. The large amount of sediment carried 
in streams immediately after a rain, especially in smnmer, 
gives some idea of the extent of this shifting. This affects 
chiefly the surface soil, and thereby brings the subsoil 
into the range of root action. 

There is little doubt that a moderate supply of plant- 
food materials will always be available in most soils, but 
for progressive agriculture manures must be used. 



CHAPTER XX 
ORGANISMS IN THE SOIL 

A VAST number of organisms, animal and ^Tgetable, live 
in the soil. By far the greater part of these belong to 
plant life, and these comprise the forms of greatest influ- 
ence in producing the changes in structure and composition 
that contribute to soil productiveness. Most of the 
organisms are so minute as to be seen only by the aid of 
the microscope, while a much smaller proportion range 
from these to the size of the larger rodents. They may 
thus be classed as microorganisms and macroorganisms. 
The latter class will be considered first. 

MACROORGANISMS OF THE SOIL 

Of the macroorganisms in the soil the animal forms 
belong chiefly to (1) rodents, (2) worms, and (3) insects; 
and the plant forms to (1) the large fungi and (2) plant 
roots. 

342. Rodents. — The burrowing habits of rodents — 
of which the ground squirrel, the mole, the gopher, and the 
prairie dog are familiar examples — result in the pulveri- 
zation and transfer of very considerable quantities of soil. 
While the activities of these animals are often not favor- 
able to agriculture, the effect on the character of the soil 
is rather beneficial and is analogous to that of good tillage. 
Their burrows also serve to aerate and drain the soil, and 

421 



422 SOILS: PROPERTIES AND MANAGEMENT 

in permanent pastures and meadows are of much value 
in this way. 

343. Worms. — The common earthworm is the most 
conspicuous example of the benefit that may accrue from 
this form of life. Darwin, as the result of careful measure- 
ments, states that the quantity of soil passed through 
these creatures may, in a favorable soil in a humid climate, 
amount to ten tons of dry earth per acre annually. The 
earthworm obtains its nourishment from the organic 
matter of the soil, but takes into its alimentary canal the 
inorganic matter as wtII, expelling the latter in the form 
of casts after it has passed entirely through the body. 
The ejected material is to some extent disintegrated, and 
is in a flocculated condition. The holes left in the soil 
serve to increase aeration and drainage, and the move- 
ments of the worms bring about a notable transportation 
of lower soil to the surface, which aids still more in effect- 
ing aeration. Darwin's studies led him to state that from 
one-tenth to two-tenths of an inch of soil is yearly brought 
to the surface of land in which earthworms exist in normal 
numbers. 

Instances are on record of land flooded for a consider- 
able period so that the worms were destroyed, and the 
productiveness of the soil was seriously impaired until it 
was restocked with earthworms. 

WoUny conducted experiments with soil, the soil in one 
case containing earthworms and in another case not con- 
taining them. Although there was much variation in his 
results, they were in every case in favor of the soil con- 
taining the worms, and in a number of the tests the yield 
on rich soil was several times as great as where no worms 
were present. 

Earthworms naturally seek a heavy, compact soil, and 



ORGANISMS IN THE SOIL 423 

it is in soil of this character that they are most needed 
because of the stirring and aeration they accomplish. 
Sandy soil and the soils of arid regions, in which are 
found few or no earthworms, are not usually in need of 
their activities. 

344. Insects. — There is a less definite, and probably 
less effective, action of a similar kind produced by insects. 
Ants, beetles, and the myriads of other burrowing insects 
and their larvae effect a considerable movement of soil 
particles, with a consequent aeration of the soil. At the 
same time they incorporate into the soil a considerable 
quantity of organic matter. 

345. Large fungi. — The larger fungi are chiefly con- 
cerned in bringing about the first stages in the decom- 
position of woody matter, which is disintegrated through 
the growth in its tissues of the root mycelia of the fungi. 
These break down the structure, and thus greatly facili- 
tate the work of the decay bacteria. Action of this kind 
is largely confined to the forest and is not of great im- 
portance in cultivated soil. 

Another function of the large fungi is exercised in the 
intimate, and possibly symbiotic, relation of the fungal 
hyphsB to the roots of many forest trees, in soil where 
nitrification proceeds very slowly, if at all, for nitrates are 
apparently not abundant in forest soils. This envelop- 
ing system of hyphae, which may consist of masses in a 
definite zone of the cortex with occasional filaments pass- 
ing outward into the soil, or which may surround the root 
with a dense mass of interwoven hyphse, is called mycor- 
rhiza. 

The cereal, cruciferous, leguminous, and solanaceous 
plants are not associated with mycorrhiza. Mycotrophic 
plants are usually those that live in a humous soil filled 



424 SOILS: PROPERTIES AND MANAGEMENT 

with the mycelia of fungi. It is tlioiight that the mvcor- 
rhiza aid the higher phiiits to obtain nutriment that they 
must strive for in competition with the fungi. 

Mycotrophic plants are also able to grow with a very 
small transpiration of moisture, as is well known to be 
the case with many conifers; and this restricted tran- 
spiration would doubtless result in lack of nutriment were 
it not for the assistance of the mycorrhiza. 

346. Plant roots. — The roots of plants assist in pro- 
moting productiveness of the soil both by contri})uting 
organic matter and by leaving, on their decay, openings 
which render the soil more permeable to water and which 
also facilitate drainage and aeration. The dense mass of 
rootlets, with their minute hairs that are left in the soil 
after every harvest, furnish a well-distributed supply of 
organic manure, which is not confined to the furrow slice, 
as is artificially incorporated manure. The drainage and 
aeration of the lower soil, due to the openings left by the 
decomposed roots, are of the greatest importance in heavy 
soil, and the beneficial effects of clover and other deep- 
rooted plants are due in no small measure to this function. 

MICROORGANISMS OF THE SOIL 

Of the microorganisms commonly exist- 
ing in soils, the greater part belong to 
plant rather than to animal life. Of the 
latter, the only organisms of well-known 
economical importance are the nematodes 
(Fig. 58), whose injurious effect on plant 
growth is accomplished through the for- 
mation of galls on the roots, in which the 
Fig. 58.— Ncma- young are hatched and live to sexual 

todcs entering ** . 

a plant root. maturity. 




ORGANISMS IN THE SOIL 425 

347. Plant microorganisms. — The microscopic plants 
of the soil may be classed as slime molds, bacteria, fimgi, 
and algffi. 

348. Plant microorganisms injurious to higher plants. 
— Injurious plant microorganisms are confined mostly 
to fungi and bacteria. They may be entirely parasitic in 
their habits, or only partially so. They injure plants by 
attacking the roots. Those that attack other parts of 
plants may live in the soil during their spore stage, but 
they are not strictly microorganisms of the soil. Some 
of the more common diseases produced by soil organisms 
are : wilt of cotton, cowpeas, watermelon, flax, tobacco, 
tomatoes, and other plants ; damping-off of a large num- 
ber of plants ; root-rot ; galls. 

These fungi or bacteria may live for long periods, prob- 
ably indefinitely, in the soil, if the conditions necessary 
for their growth are maintained. Some of them will die 
within a few years if their host plants are not grown on 
the soil, but others are able to maintain existence on 
almost any organic substance. Once a soil is infected, 
it is likely to remain so for a long time, or indeed indefi- 
nitely. Infection is easily carried. Soil from infected 
fields may be carried on implements, plants, or rubbish 
of any kind, in soil used for inoculation of leguminous 
crops, or even in stable manure containing infected plants 
or in the feces resulting from the feeding of infected plants. 
P'looding of land by which soil is washed from one field 
to another may be a means of infection. 

Prevention is the best defense from diseases produced 
by these soil organisms. Once disease has procured a 
foothold, it is practically impossible to eradicate all its 
' organisms. Rotation of crops is effective for some dis- 
eases, but entire absence of the host crop is oftener neces- 



426 soils: properties and management 

sary. The use of lime is beneficial in the case of certain 
diseases. Chemicals of various kinds have been tried 
with little success. Steam sterilization is a practical 
method of treating greenhouse soils for a number of dis- 
eases. The breeding of plants immune to the disease af- 
fecting its particular species has been successfully carried 
out in the case of the cowpea and cotton plants, and can 
doubtless be accomplished with others. 

In regions in which farming is confined largely to one 
crop or to a limited number of cereals, it is the common 
experience that yields decrease greatly in the course of a 
score of years after the \'irgin soil is broken. The cause 
for this is attributed by Bolley ^ in large measure to a 
diseased condition of the plants due to the growth of 
various fungi that inhabit the soil and attack the crops 
grown on it. He reports that he has experimented with 
pure cultures taken from wheat grains, straw, and roots, 
and has demonstrated that certain strains or species of 
Fusarium, Helminthosporium, Alternaria, iNIacrosporium, 
CoUetotrichum, and Cephalothecium are directly capable 
of attacking and destroying growing plants of wheat, oats, 
barley, brome grass, and quack grass, and that within 
limits the disease may be transferred from one type of 
crop to another. 

349. Plant microorganisms not injurious to higher 
plants. — The vegetable microorganisms of the soil all 
take an active part in removing dead plants and animals 
from the surface of the soil, and in bringing about the other 
operations that are necessary for the production of plants. 
The first step in the preparation for plant growth is to 
remove the remains of plants and animals that would 

> Bolley, H. L. Wheat. North Dakota Agr. Exp. Sta., 
Bui. 107. 1913. 



ORGANISMS IN THE SOIL 427 

otherwise accumulate to the exclusi(jn of other plants. 
These are decomposed through the action of organisms 
of various kinds, the intermediate and final products of 
decomposition assisting plant production by contributing 
nitrogen and certain mineral compounds that are a 
directly available source of plant nutriment, and also by 
the effect of certain of the decomposition products on the 
mineral substances of the soil, by which they are rendered 
soluble and hence available to the plant. 

Through these operations the supply of carbon and 
nitrogen required for the production of organic matter is 
kept in circulation. The complex organic compounds 
in the bodies of dead plants or animals, in which condi- 
tion plants cannot use them, are, under the action of 
microorganisms, converted by a number of stages into 
the very simple compounds used by plants. In the course 
of this process a part of the nitrogen is sometimes lost 
into the air by conversion into free nitrogen, but fortu- 
nately this may be recovered and even more nitrogen 
taken from the air by certain other organisms of the soil. 

The slime molds, bacteria, fungi, and algae all play a 
part in these processes, but none of them so actively 
during every stage of the processes as do the bacteria. 
Molds and fungi are particularly active in the early stages 
of decomposition of both nitrogenous and non-nitrogenous 
organic matter. ]Molds are also capable of ammonifying 
proteins, and even re-forming the complex protein bodies 
from the nitrogen of ammonium salts. Certain of the 
molds and of the algae are apparently able to fix atmos- 
pheric nitrogen, and contribute a supply of carbohydrates 
required for the use of the nitrogen-fixing bacteria. Among 
these are Aspergillus niger and PenicUlium glaucum. 

It also seems probable that the fungi associated with 



428 SOILS: PEOPEHTIES AND MANAGEMENT 



the roots of many forest trees and known as mycorrhizal 
fungi liave the abihty to fix atmospheric nitrogen, and that 
in some way the trees obtain a part, at least, of the nitro- 
gen so fixed. The growth of forests on poor, sandy soil 
containing practically no nitrogen has been urged as an 
example of this process. 

350. Bacteria. — Of the several forms of microorgan- 
isms found in the soil, bacteria are the most important. 
In fact, the abundant, and continued growth of plants on 
the soil is absolutely dependent on the presence of bacteria, 
for through their action chemical changes are brought 
about which result in making soluble both organic and 
inorganic material necessary for the life of higher plants, 
and which, in part at least, would not otherwise occur. 

Bacteria are thus trans- 
formers, not producers, of 
fertility in the soil, although, 
as will be seen later, certain 
kinds of bacteria take nitro- 
gen from the air and leave it 
in the soil. With this excep- 
tion, however, they add no 
plant-food to the soil. It is 
their action in rendering 
available to the plant ma- 
terial already present in the 
soil that constitutes their 
greatest present value in crop 
production. It is to their 
activity in conveying nitro- 
gen from the air to the soil 
that we are indebted for most of our supply of nitrogen 
in virgin soils (see Fig. 59). 




Fig. 59. — Some types of soil mi- 
croorganisms highly magnified, 
(a) , nitrate formers ; (b) , ni- 
trite formers; (c), B. graveo- 
lens ; [d) , B. fusiformis ; (e) , B. 
subtilis ; (/), Clostridium pas- 
torianum. 



ORGANISMS IN TUE SOIL 429 

It is not usually the entire absence of bacteria from the 
soil that is to be avoided in practice, for all arable soils con- 
tain bacteria, although sometimes not all of the desirable 
forms ; but, as great bacterial activity is required for the 
large production of crops, the practical problem is to main- 
tain a condition of soil most favorable to such activity. 

351. Distribution of bacteria. — Bacteria are found 
almost universally in soils, although they are much more 
numerous in some soils than in others. A number of in- 
vestigators have stated that in soils from different locali- 
ties and of different types that they have examined, the 
numbers of bacteria were proportional to the productive- 
ness of the soils. The number of bacteria present has in 
some cases been shown to be proportional to^the amount 
of humus contained in the soil. It is natural to expect 
that within certain limits both these findings will hold. The 
conditions obtaining in a productive soil are those favorable 
to the development of certain forms of bacteria, and these 
kinds constitute a very large proportion of those generally 
found in soils. However, there is evidence that compara- 
tively unproductive soils may contain a large number of 
bacteria that are presumably not favorable to plant growth. 

Samples of soil taken from certain productive and rela- 
tively unproductive parts of a field on the Cornell Uni- 
versity farm contained a larger number of bacteria in the 
poor soil, although the two soils were equally well drained 
and the good soil had slightly more organic matter. 
They had also received practically the same treatment 
during the preceding few years : — 

Character of Number of bacteria 

soil per gram of dry soil 

Good 1,200,000 

Poor 1,600,000 



430 SOILS: PROPERTIES AND MANAGEMENT 

After wheat had been growing for two months on these 
soils in the greenhouse, the soils being maintained at the 
same moisture content, the samples showed the following 
count : — 

Character of Number of bacteria 

soil to a gram of dry soil 

Good 7()(),()()0 

Poor 1,12(),(){)() 

Another reason why this relation between the number 
of bacteria and soil productiveness does not hold is that 
the bacteria having the same functions in relation to plant- 
food do not always have the same physiological efficiency. 
In other words, they do not have the same virulence, a 
small number in some cases being able to bring about the 
same changes that in other cases require a much greater 
number. 

Bacteria are found chiefly in the upper layers of soil, 
although not in large numbers at the immediate surface 
of the ground. In humid regions the layer between the 
first inch and the sixth or the seventh inch contains, in 
most soils, the great bulk of bacteria present. In arid or 
semiarid regions, bacteria are found at greater depths 
and the densest population is located at loAver levels than 
in humid regions. This is largely because of the deeper 
penetration of the air and the conditions that accom- 
pany it. 

352. Numbers of bacteria. — The number of bacteria in 
a soil will naturally vary with the conditions that favor or 
discourage their growth. In very sandy soils, forest soils, 
desert soils, water-logged soils, and soils low in humus, 
the bacteria are either absent or comparatively few in 
numbers. In soils very rich in organic matter, especially 



ORGANISMS IN THE SOIL 431 

where animal manure has been applied or where a carcass 
has been buried, the number becomes very large, as 
many as 100,000,000 to a gram of soil having been found ; 
while in soil of ordinary fertility and tilth the numbers 
range from 1 ,000,000 to 5,000,000 to a gram. The extreme 
rapidity with which reproduction occurs makes it possible 
for the number to increase enormously when conditions 
are favorable for their growth. 

The table on page 432 shows the number of bacteria 
to a gram of soil found in different parts of the United 
States during some portion of the growing season. 

The figures showing the number of bacteria in each 
gram of soil that are presented in this table cannot be 
used for a comparison of the relati\'e numbers of bacteria 
in soils of different regions of this country, because dif- 
ferent methods were used by the experimenters in making 
the estimations. They are, how^ever, an indication of 
what may be considered the ordinary range in arable 
soils. 

353. Numbers as influenced by season. — It might be 
supposed that, like most plants, bacteria would develop 
most rapidly in summer months and that they would be 
found in largest numbers at that season, at least in regions 
of low temperatures during the winter months. That 
this is not always the case has been showm by Conn,^ 
who found as the result of periodical enumeration of bac- 
teria throughout a term of two years that the highest 
counts were obtained during the w^inter months, when 
the soil was frozen. This does not mean that all classes 
of bacteria are present in largest numbers at that season, 
but, as explained by Conn, it seems likely that certain 

1 Conn, H. J. Bacteria in Frozen Soils II. Centrlb. f. 
Bakt., II, Band 32, Seite 70-97. 1912. 



432 SOILS: PROPERTIES AND MANAGEMENT 



NuMBEu OF Bacteria to a Guam of Soil during Some 
Period of the Growing Season 



State 


Soil 


Depth 


Crop 


Investi- 
gator 


Number 

OF 

Bacteria 


Delaware . 


Stiff clay 


3 

inches 


Orchard in high 
state of culti- 
vation. In 
cover crops 


Chester ' 


2,200,000 


Delaware . 


Adjoining soil above 


3 


Meadow for 


Chester ' 


450,000 




and of same char- 


inches 


twelve years 








acter 










Delaware . 


Of same type as 


3 


Vegetables and 


Chester i 


1,800,000 




above 


inches 


heavily ma- 
nured 






Delaware . 






Scarlet clover 


Chester » 


3,360,000 








plowed under 












and alter- 












nated with 












maize for ten 












.\-ears 






Kansas 


Loam, rich in humus 


30 


Alfalfa, five 


Mayo and 


33,931,808 






inches 


years 


Kinsley ^ 




Kansas 


Loam, richer in hu- 


30 


Alfalfa 


Mayo and 


53,596,060 




mus than soil above 


inches 




Kinsley » 




Kansas 


Thin soil, gumbo 


30 


Mixed grasses 


Mayo and 


78,534 




subsoil 


inches 




Kinsley ^ 




Kansas 


Loam, low in humus 


30 
inches 


Oats and wheat 


Mayo and 
Kinsley - 


8,543,006 


Iowa 


Marshall loam, no 
lime applied 


top 
soil 


Oats 


Brown ' 


1,930,000 


Iowa . . 


Marshall loam, 1,000 
pounds lime per 
acre 


top 
soil 


Oats 


Brown ' 


2,342,000 


Iowa . . 


Marshall loam. 2,000 
pounds lime per 
aero 


top 
soil 


Oata 


Brown ' 


2,787,000 


Iowa . . 


Marshall loam, 6,000 
pounds lime per 
acre 


top 

soil 


Oats 


Brown ' 


3,766,000 



1 Chester, F. D. The Bacteriological Analysis of Soils. 
Delaware Agr. Exp. Sta., Bui. Go. 1904. 

2 Mayo, U. S., and Kinsley, A. F. Bacteria of the Soil. 
Kansas Agr. Exp. Sta., Bui. 117. 1903. 

■' Brown, P. E. Some Bacterial Effects of Liming. Iowa 
Agr. Exp. Sta., Research Bui. 2. 1911. 



ORGANISMS IN THE SOIL 



433 



forms predominate in summer and others in winter (see 
Fig. 60). 




Fig. 60. — Periodical enumeration of bacteria in soil of two plats during 
two years, expressed in millions to a gram of dry soil. 

Brown and Smith ^ obtained results that in the main 
confirmed Conn's work, and they advanced the theory 
that the concentration of the soil solution immediately 
surrounding the soil particles, together with the high 
surface tension exerted by the soil particles, prevents the 
freezing of the surface film and that this water forms a 
suitable medium for the development of bacteria. 

354. Conditions affecting growth. — jNIany conditions 
of the soil affect the growth of bacteria. Among the most 
important of these are the supply of oxygen and moisture, 
the temperature, the presence of organic matter, and the 
acidity or the basicity of the soil. 

355. Oxygen. — All soil bacteria require for their 
growth a certain amount of oxygen. Some bacteria, how- 
ever, can continue their activities with much less oxygen 
than can others. Those requiring an abundant supply 
of oxygen have been called aerobic bacteria, while those 
preferring little or no air are designated as anaerobic 

1 Brown, P. E., and Smith, R. E. Bacterial Activities in 
Frozen Soil. Iowa Agr. Exp. Sta., Research Bui. 4. 1912. 

2f 



434 SOILS: PROPERTIES AND MANAGEMENT 

bacteria. This is an important distinction, because those 
bacteria that are of the greatest benefit to the soil are, in 
the main, aerobes, and those that are injurious in their 
action are chiefly anaerobes. However, it seems hkely 
that an aerobic bacterium may gradually accommodate 
itself within certain limits to an environment containing 
less oxygen, and an anaerobic bacterium may accommo- 
date itself to the presence of a larger amount of oxygen. 
Thus a bacterium may be most active in the presence of 
an abundant supply of oxygen, but, when subjected to 
conditions in which the supply is small, growth continues 
but with lessened vigor. The term facultative bacteria 
has been used to designate those bacteria that are able 
to adapt themselves to considerable \ariation in oxygen 
supply. The structure, tilth, and drainage of the soil 
consequently determine largely whether aerobic or an- 
aerobic bacteria shall be more active. 

356. Moisture. — Bacteria require some moisture for 
their growth. A notable decrease in the moisture con- 
tent of the soil may temporarily decrease the number of 
bacteria by limiting their (le\elopment to the films of 
moisture surrounding the particles. With a decrease in 
the moisture content of a soil, there occurs an increase 
in the oxygen in the interstitial spaces. Those bacteria 
that thrive in the presence of oxygen are thereby favored, 
and the character of the bacterial flora is correspondingly 
changed. When the soil remains saturated, or nearly 
so, for any considerable period, the anaerobic forms 
assert themselves, and the usually beneficial activities 
of the aerobic bacteria are temporarily suspended. 
The most favorable moisture condition for the activity 
of the most desirable bacteria is that found in a well- 
drained soil. 



ORGANISMS IN THE SOIL 435 

357. Temperature. — Soil bacteria, like other plants, 
continue life and growth under a considerable range of 
temperature. Freezing, while rendering bacteria dor- 
mant, does not kill them, and growth begins slightly 
above that point. It has been show^n that nitrification 
goes on at temperatures as low as from 37° to 39° F. It 
is not, however, until the temperature is considerably 
higher that their functions are pronounced. From 70° 
to 110° F. their activity is greatest, and it diminishes 
perceptibly below or above those points. The thermal 
death point of most forms of bacteria is found at some 
point between 110° and 160° F., but the spore forms even 
resist boiling. Only in some desert soils does the natural 
temperature reach a point sufficiently high to actually 
destroy bacteria, and there only near the surface. In fact, 
it is seldom that soil temperatures become sufficiently high 
to curtail bacterial activity. 

358. Organic matter. — The presence of a certain 
amount of organic matter is essential to the growth of 
most, but not all, forms of soil bacteria. The organic 
matter of the soil, consisting as it does of the remains of 
a large variety of substances, furnishes a suitable food 
supply for a very great number of forms of organisms. 
The action of one set of bacteria on the cellular matter of 
plants embodied in the soil produces compounds suited to 
other forms, and so from one stage of decomposition to 
another this constantly changing material affords sus- 
tenance to a bacterial flora the extent and variety of which 
it is difficult to conceive. Not only do bacteria aflfect the 
organic matter of the soil, but, in the case of certain 
forms, their activities produce changes in the inorganic 
matter that cause it to become more soluble and more 
easily available to the plant. 



436 SOILS: PROPERTIES AND MANAGEMENT 

A soil low in organic matter usually has a lower bac- 
terial content than one containing a larger amount, and, 
under favorable conditions, the beneficial action, to a cer- 
tain point at least, increases with the content of organic 
substance; but, as the products of bacterial life are 
generally injurious to the organisms producing them, 
such factors as the rate of aeration and the basicity of 
the soil must determine the effectiveness of the organic 
matter. 

359. Soil acidity. — A soil having an acid reaction 
makes a poor medium for the growth of certain bacteria. 
A neutral or a slightly alkaline soil furnishes the most 
favorable condition for the development of the forms of 
bacteria most beneficial to arable land. The activities of 
many soil bacteria result in the formation of acids which 
are injurious to the bacteria themselves, and, unless there 
is present some basic substance with which these can 
combine, bacterial development is inhibited by their own 
products. This is one of the reasons why lime is so often of 
great benefit when applied to soils, and especially to those 
on which alfalfa and red clover are growing. For the 
same reason, the presence of lime hastens decay of or- 
ganic matter in certain soils, and the conversion of nitrog- 
enous material with a minimum loss into compounds 
available to the plants. As showing the value of lime 
in the process of nitrate formation, it has been pointed 
out that in the presence of an adequate supply of lime 
the availability of ammonium salts is almost as high 
as that of nitrate salts, but where the supply of lime 
is insufficient the value of ammonium salts is relatively 
rather low. 

360. Functions of soil bacteria. — Bacteria have a part 
in many of the processes of the soil which greatly aftects 



ORGANISMS IN THE SOIL 437 

its productiveness. It has become customary to refer to 
the changes produced by certain forms of bacteria as their 
function in contributing to soil productiveness. 

361. Decomposition of mineral matter. — Certain bac- 
teria decompose some of the mineral matter of the 
soil and render it more easily available to the plant. 
While the nature of the processes and their extent 
are not known, there is sufficient evidence to justify 
the above statement. It is well known that several 
forms of bacteria are instrumental in decomposing rock, 
and that sulfur and iron compounds are acted upon by 
other forms. 

To what extent the very difficultly soluble forms of 
phosphorus, as tricalcium phosphate for example, are 
rendered soluble and available to agricultural plants by 
microorganisms, is a matter of great importance. The 
extent to which the subject has been investigated is 
rather limited, but, in the main, there is indicated a con- 
siderable action of both bacteria and fungi on tricalcium 
phosphate. 

362. Influence of certain bacteria and molds on the 
solubility of phosphates. — Some very significant experi- 
ments were performed by Stoklasa, Duchacek, and Pitra,^ 
who found that bone meal, when brought into contact 
with pure cultures of certain bacteria, was apparently 
rendered soluble, the extent to which the solubility pro- 
gressed varying with the different forms of bacteria 
brought into contact with it. The percentage of the total 
phosphorus in the meal that was rendered soluble was as 
follows : — 

> Stoklasa, J., Duchacek, F., and Pitra, J. Uber den Einfluss 
der Bakterien auf die Knochenzersetzung. Centrlb. f. Bakt., 
II, Band 6, Seite 526-535, 554-558. 1900. 



438 SOILS: PROPERTIES AND MANAGEMENT 

Per cent 

Not inoculated 3.83 

B. megatherium 21.56 

B. fluorescens 9.19 

B. proteus vulgaris 14.79 

B. butyricus Hueppe 15.55 

B. mycoides 23.03 

B. mesentericus 20.60 

Lohnis ^ quotes Grazia e Cerza to have found that 
Aspergillus uiger, Penicillunn glaiiciini, and P. brevicaule, 
isolated from garden soil, when j)laced in nutrient solu- 
tion with tricalcium phosphate, assimilated one-fifth to 
one-third of the phosphorus in sixty days. 

There is some difference of opinion whether the solvent 
action arising from bacterial growth is due entirely to the 
acids that are produced by the bacteria exerting such 
action, or whether there is also some other influence exer- 
cised by bacteria. Stoklasa accounts for the solvent 
action of the bacteria in his experiments by the bacterial 
secretion of proteolytic and diastatic enzymes acting on 
the bone meal. In opposition to this idea, Krober - 
maintains that the solvent action depends on the kind of 
fermentation that the organic matter undergoes, acid fer- 
mentation rendering the phosphates more soluble, while 
ammoniacal fermentation results in no solvent action on 
tricalcium phosphate and, in the presence of sufficient 
basic material, may render the monocalcium and dical- 

1 Lohnis, F. Handbuch d. Landw. Bakteriologie, Seite 700. 
Berlin. 1910. 

2 Krober, E. Uber das Loslichwerden der Phosphorsaure 
aus Wasserunlosliclien Verbindungen unter der Einwirkung von 
Bakterien und Hefen. Jour. f. Landw., Band 57, Seite 5-80. 
1909-1910. 



ORGANISMS IN THE SOIL 439 

cium phosphates insohible. He would Hmit the solvent 
action of bacteria to the effect of the acids they produce. 

Sackett, Patten, and Brown ^ have in a measure repeated 
Stoklasa's experiments and obtained somewhat similar 
results, which lead them to conclude that there is a 
solvent agent other than the acids produced by the 
bacteria. 

It would appear from these experiments that bacteria, 
and possibly fungi, commonly found in soils act on tri- 
calcium phosphate in such a manner as to render a part 
of it soluble. Nevertheless, experiments that have been 
conducted for the purpose of ascertaining whether tri- 
calcium phosphate in soils is rendered more readily avail- 
able to plants when large quantities of decomposing organic 
matter are present than when this is not the case, have 
not, in the main, indicated that the decomposing organic 
matter increases availability of the phosphorus (par. 439). 
An explanation of this may possibly be found in the 
occurrence of a reverse biological process which results 
in the transformation of soluble phosphates into insoluble 
ones, the occurrence of such a process having been found 
by Stoklasa ^ and others. 

The carbon dioxide produced by bacteria is a solvent 
for many of the silicates of the soil, and may free calcium 
and potassium from hornblende and feldspar. 

Various groups of sulfur bacteria, through the produc- 
tion of H2S and H2SO4, act on iron in the soil and con- 
vert it into sulfide and sulfate. Carbon dioxide also 

1 Saekett, W. G., Patten, A. J., and Brown, C. W. The 
Solvent Action of Soil Bacteria upon the Insoluble Phosphates 
of Raw Bone Meal and Natural Rock Phosphate. Michigan 
Agr. Exp. Sta., Special Bui. 43. 1908. 

2 Stoklasa, J. Biochemiseher Kreislauf des Phosphat-Ions 
im Boden. Centrlb. f. Bakt., II, Band 29, Seite 385-519. 1913. 



440 SOILS: PROPERTIES AND MANAGEMENT 

plays a part in the solution of iron. The lower fungi and 
the algie precipitate iron from solution as iron oxide. 

363. Decomposition of non-nitrogenous organic matter. 
— The organic matter commonly decomposed in soils 
contains a large proportion of compounds containing no 
nitrogen. Many non-nitrogenous substances decompose 
rather rapidly, and the organic nitrogen disappears less 
rapidly than the carbon, hydrogen, and oxygen of organic 
bodies. 

Humus always contains a higher percentage of nitrogen 
than do the plants from which it is formed. 

The non-nitrogenous substances consist of cellulose and 
allied compounds forming the cell walls of plants, and the 
carbohydrates, organic acids, fats, and the like, contained 
in them. The dissolution of cellulose is brought about 
by the action of the enzyme cytase secreted by a number 
of fungi, and is also probably accomplished by the Bacillus 
amylohacter, but whether through the secretion of an 
enzyme is not known. Other bacteria have been reported 
to secrete a cytase that acts on certain constituents of the 
cell wall. It is probable that numerous organisms capa- 
ble of fermenting cellulose and allied substances exist in 
the soil, accomplishing this decomposition through the 
production of cytase. 

The effect of cytase on cellulose and other fiber is to 
hydrolyze it with the formation of sugar, as glucose, 
mannose, zylose, arabinose, and the like. 

Starch is converted into glucose by a ferment (diastase) 
either present in the plant itself or possibly secreted by 
fungi or bacteria. All the sugars are finally converted 
into organic acids which may combine with mineral bases. 
Distinct organisms have been isolated that can utilize 
for their development formates, acetates, propionates. 



ORGANISMS IN THE SOIL 441 

butyrates, and the like, the final product being carbon 
dioxide and water. Thus, step by step, the non-nitroge- 
nous matter incorporated with the soil is carried by 
one and anotlier form of organism from the most com- 
plex to the simplest combinations. 

The final product of the decomposition of carbonaceous 
matter being carbon dioxide, there is a return to the air 
of the compound from which the carbon of the decompos- 
ing substance was originally derived. In the plant, un- 
less it is saprophytic, the carbon of the tissues comes 
largely from the carbon dioxide of the air, from which 
more complex carbon-bearing compounds are produced and 
utilized in its functions or in its tissues. A portion of the 
carbon is returned to the air by the plant in the form of 
carbon dioxide ; the remainder is retained by the plant, 
and may be returned by the process of decay or may be 
consumed by an animal, and, as the result of its physio- 
logical processes, either exhaled as carbon dioxide or 
deposited in the tissues to be later decomposed and con- 
verted into carbon dioxide. The soil is thus the scene of 
at least a part of the varied transformations through 
which carbon is continually passing as it is utilized by 
higher plants, animals, bacteria, and fungi. 

The non-nitrogenous organic substances in their various 
stages furnish food for a large number of bacteria, among 
which are those concerned in the decomposition of mineral 
matter and in the processes of nitrification and nitrogen 
fixation. There are, therefore, two ways in which these 
substances are of great importance in soil fertility : (1) as 
a source of carbon dioxide and of organic acids; (2) as 
a food supply for useful soil bacteria. 

364. Decomposition of nitrogenous organic matter. — 
The decomposition of nitrogenous organic matter is ac- 



442 SOILS: PROPERTIES AND MANAGEMENT 

complislierl by a series of changes from one compound to 
another, as was seen to be the case with the non-nitroge- 
nous materials. The final products are carbon dioxide, 
water, usually some hydrocarbon gases resulting from 
the carbon and hydrogen of the organic matter, and also 
some hydrogen sulfide or other gas containing sulfur 
or a final oxidation of the sulfur of the proteidS into sul- 
fates ; while the nitrogen is ultimately converted into 
nitrates, or into free nitrogen, although a portion of the 
original nitrogen sometimes escapes into the air in the 
intermediate stage, ammonia. 

The processes will be discussed under the following 
heads, which represent certain more or less definite stages 
in the decomposition: 1, decay and putrefaction; 2, am- 
monification ; 3, nitrification ; 4, denitrification ; 5, fixa- 
tion of atmospheric nitrogen. These various processes 
form what has been termed the nitrogen cycle. 



CHAPTER XXI 
THE NITROGEN CYCLE 

Of the various elements composing the nutrients used 
by phmts, nitrogen has the highest commercial value. 
It is, moreover, absorbed in large quantities by agricul- 
tural plants and the supply is constantly liable to loss in 
drainage water and in the gaseous form. Its importance 
to agriculture has led to much study of its occurrence, 
combinations, reactions, and movements in the soil. 

When it is recalled that the nitrogen gas of the atmos- 
phere is the one p^imiti^'e source of the world's supply of 
nitrogen, it becomes apparent that the agencies that have 
been instrumental in its transfer from one condition to 
another have been extremely active. The movement of 
nitrogen from air to soil, from soil to plant, from plant 
back to soil or to animal, and from animal back to soil, 
with a return to air at various stages, involves many 
forces, many factors, many organisms, and many re- 
actions. 

365. Decay and putrefaction. — Decomposition of the 
nitrogenous organic matter of the soil, consisting largely 
of the proteins, begins with either one of two processes 
— decay or putrefaction. Decay is produced by aerobic 
bacteria, and naturally occurs when the conditions are 
most favorable for their development. When the condi- 
tions are otherwise, the growth of these bacteria is checked, 
and then further decomposition would be extremely slow 

443 



444 SOILS: PROPERTIES AND MANAGEMENT 

were it not for the other proeess — putrefaction. Putre- 
faction is produced by anaerobic bacteria. In the same 
body, and consequently in the same soil, decay and putre- 
faction may be in progress simultaneously, decay taking 
place on the outside and on the surfaces of other parts 
exposed to the air, while putrefaction occurs on the in- 
terior, where the supply of oxygen is limited. By means 
of the two processes, decomposition is greatly facilitated. 
Decay (see Fig. 61) produces a very rapid and complete 
decomposition of the substance in which it operates, most 
of the carbon and hydrogen being quickly converted into 
carbon dioxide and water, and the nitrogen into ammonia 
and probably some free nitrogen. The latter is possibly 
due to the oxidation of ammonia, thus 

4 NHs + 3 O2 = 6 H2O + 2 N2 

The sulfur of the proteins finally appears in the form of 
sulfates. 

What the intermediate products are has not been deter- 
mined, but in the decay of meat, in which there was an 
abundant supply of oxygen, succinic, palmytic, oleic, and 
phenyl-propionic acids have been found. 

Putrefaction results in a large number of complex inter- 
mediate compounds and proceeds much more slowly. 
Many of the substances thus produced are highly poison- 
ous, and most of them have a very offensive odor. They 
may be further broken down by decay when the condi- 
tions are suitable, or by a continuation of the process of 
putrefaction. In either case, the poisonous properties 
and the odor are removed. 

In the process of decomposition of organic matter two 
classes of substances are produced : (1) those that have 
been excreted or secreted h\ the bacterium, and therefore 



THE NITROGEN CYCLE 445 

have passed through the metaboHc processes of the organ- 
ism ; (2) those that ha\'e been formed because of the 
removal of certain atoms by bacteria or enzymes from 
compounds, thus necessitating a readjustment of the 
remaining atoms and the consequent formation of a new 
compound. 

Putrefaction is carried on by a large number of forms 
of bacteria, the resulting product depending on the sub- 
stance in process of decomposition and on the bacteria 
involved. Some of the characteristic, although not con- 
stant, products formed in the putrefaction of albumin 
and proteins are albumoses, peptones, and amino acids, 
followed by the formation of cadaverine, putrescine, ska- 
tol, and indol. Where an abundant supply of oxygen is 
present, or where a sufficient supply of carbohydrates 
exist, these substances are not formed. There are many 
other products of putrefaction, including a number of 
gases, as carbon dioxide, hydrogen sulfide, marsh gas, 
phosphine, hydrogen, nitrogen, and the like. 

It will be noticed that these changes, like those occur- 
ring in the non-nitrogenous organic matter, involve a 
breaking-down of the more complex compounds and the 
formation of simpler ones ; and that a very large number 
of bacteria are concerned in the various steps, while even 
the same substances may be decomposed and the same 
resulting compounds formed by a number of different 
species of bacteria. 

Present-day knowledge of the subject does not make 
it possible to present a list of the bacteria concerned in 
each step, or to name all the intermediate products 
formed ; but for the student of the soil the principal 
consideration is a knowledge of the circumstances under 
which the nitrogen is made available to plants, and the 



446 SOILS: PROPERTIES AND MANAGEMENT 

conditions that are likely to result in its loss from the 
soil. 

366. Ammonification. — Decay and putrefaction may 
be considered as the heginninf;^ of the process of ammoni- 
fication. iVmmonification (see Fig. 61), as its name 
implies, is that stage of the process during which am- 
monia is formed from the intermediate products. 

Like the other processes of decomposition, there are 
many species of bacteria capable of forming ammonia 
from nitrogenous organic substances. Different forms 
display diflerent abilities in converting nitrogen of the 
same organic material into ammonia, some acting more 
rapidly or more thoroughly than others. In tests by 
certain investigators in which the same bacteria are used 
on different substances, the order of their efficiency is 
changed with the change of substance. It seems likely, 
therefore, that certain forms are most efficient when 
acting on certain organic compounds ; that, in other 
words, each sf)ecies is best adapted to the decom- 
position of certain substances, while capable of attack- 
ing others although less eft'ectively. This characteristic 
preference of a class of bacteria for the decomposition of 
certain substances is made e\ident by the experiments 
of Sackett/ who found that in some soils dried blood was 
ammonified more rapidly than was cottonseed meal, while 
in other soils the reverse was true. 

367. Bacteria ana substances concerned in ammoni- 
fication. — Among the bacteria producing ammonifica- 
tion arc JL uiycoidcs, B. subtili.s', B. mesentcrims vul- 
gatus, B. jantlimus, and B. protcua vulgaris. Of these, 
B. mycuides has been very carefully studied, and the 

' Sackett, W. G. The Ammonifying Efficiency of Certain 
Colorado Soils. Colorado Agr. Exp. Sta., Bui. 184. 1912. 



THE NITROGEN CYCLE 447 

findings of Marchal ^ may be taken as representative 
of the process of ammonification. He found that when 
this bacterium was seeded on a neutral solution of albumin, 
ammonia and carbon dioxide were produced, together 
with small amounts of peptone, leucine, tyrosine, and 
formic, butyric, and propionic acids. He concludes that 
in the process, atmospheric oxygen is used, and that 
the carbon of the albumin is converted into carbon dioxide, 
the sulfur into sulfuric acid, and the hydrogen partly 
into water, and partly into ammonia by combining 
with the nitrogen of the organic substance. He suggests 
that a complete decomposition of the albumin occurs 
according to the following reaction : — 

C72H112 NisSOaa + 77 O2 

= 29 H2O + 72 COo + SO3 + 18 NH3 

The greatest activity occurred at a temperature of 86° 
F., and as low as 68° F. action was rather strong. Access 
of an increased amount of air, produced by increasing the 
surface of the liquid, increased the rate of ammonification. 
A slightly acid reaction in the liquid produced the maxi- 
mum activity, but in a neutral or even slightly acid me- 
dium the process was continued, although much less 
actively. 

]\Iarchal found that B. mycoides was also capable of 
ammonifying casein, fibrin, legumin, glutin, myosin, 
serin, peptones, creatine, leucine, tyroGine, and asparagine, 
but not urea. 

368. Nitrification. — Some agricultural plants can util- 
ize ammonium salts as a source of nitrogen. This has 

1 Marchal, E. Sur la Production de rAmmoniaqiie dans 
le Sol par les Microbes. Bulletins do I'Acad. Royale de Belg., 
3 series, F. 25, pp. 727-77G. 1893. 



448 SOILS: PROPERTIES AND MANAGEMENT 

been determined for maize, rice, peas, barley, and po- 
tatoes. Other plants, such as beets, show a decided 
preference for nitrogen in the form of nitrates. Whether 
any of the common crops can thrive as well on ammo- 
nium salts as on nitrates has not been finally demon- 
strated. In most arable soils the transformation of nitro- 
gen does not stop with its conversion into ammonia, l)ut 
goes on by an oxidation process to the formation of first 
nitrous, and then nitric, acids (see Fig. 61). This may be 
considered to proceed according to the following equa- 
tions : — 

2 NHg + 3 O2 - 2 HNO2 + 2 H2O 

2 HNO2 + O2 = 2 HNO3 

The acid in either case combines with one of the bases 
of the soil, usually calcium, so that calcium nitrate 
results. 

Each of these steps is brought about by a distinct 
bacterium, but the bacteria are closely related. Collec- 
tively they are called nitrobacteria. Nitrosomonas and 
Nitrosococcus are the bacteria concerned in the conver- 
sion of ammonia into nitrous acid or nitrites. The former 
are supposed to be characteristic of European, and the 
latter of American, soils. They are sometimes referred 
to as nitrous ferments. 

Nitrobacter are those bacteria that convert nitrites 
into nitrates. They are also designated nitric ferments. 
There seem to be some difierences in bacteria from dif- 
ferent soils, but the differences are slight and the condi- 
tions favoring the actions of the bacteria are similar. It 
is also true that the conditions favoring the action of 
Nitrosomonas and Nitrobacter are similar, and they 
are generally found in the same soils, although some 



TEE NITROGEN CYCLE 



449 



experiments show that in the same soil nitrites may 
sometimes accumulate, indicating conditions more favor- 
able to the development of the Nitrosomonas bacteria. 



*■ To amma/ 




. Green /^arm 
' /y~ee /?/^rofe// ' ' como/ex /V- compounJT—,— " 4- 



^MMon/ncA r/ON 



Fig. 61. — Diagrammatic representation of the movements of nitrogen 
between soil, plant, animal, and atmosphere. This has been termed 
the nitrogen cycle. 

The formation of nitrates usually follows closely on the 
production of nitrites, so that there is rarely more than 
a trace of the latter to be found in soils. A soil favorable 
to the process of nitrification is usually well adapted to 
all the processes of nitrogen transformation. 

Marked differences have been found in the nitrifying 
power of bacteria from different soils. Highly productive 
soils have generally been found to contain bacteria having 
greater nitrifying efficiency than those from less produc- 
tive soils, but this may not always be the case, as other 
factors may limit the productiveness. 

369. Effect of organic matter on nitrification. — A 
peculiarity in the artificial culture of nitrifying bacteria 
2g 



450 SOILS: PROPERTIES AND MANAGEMENT 

is that they cannot be grown in artificial media containing 
organic matter. This property for a long time prevented 
the isolation and identification of these organisms, as it 
was hardly concei\able that organisms living in the dark, 
where energy cannot be obtained from sunlight, could 
exist without using the energy stored by organic matter. 
It has been suggested, in explanation of this, that the 
energy produced by the oxidation involved in the process 
of nitrification makes possible the growth of the organisms 
under these apparently impossible conditions. Some 
experimenters report having grown nitrobacteria in or- 
ganic media, but it is generally believed at present that 
this is not possible and that there has been some error in 
the work of these experimenters. 

The presence of peptone in the proportion of 500 
parts per million completely prevents the development 
of nitrobacteria, and one-half that quantity checks it ; 
while 150 parts of ammonia to the million has a similar 
effect. In a normal soil the quantity of soluble ammo- 
nium salts is well below this amount, as must also be that 
of soluble organic matter. In confirmation of the inhibit- 
ing effect of organic matter on the nitrobacteria, cases 
have been reported of soils very rich in organic matter 
in which no bacteria of this type exist. 

It has also been stated that very heavy manuring 
with organic manures results in decreased nitrification 
in the soil. While this may be true where farm manure 
is used in the quantities sometimes applied- in gardening 
operations, it is not likely to be the case in soils on which 
ordinary field crops are grown. The principle is well 
illustrated by the dry-earth closet. Manure mixed with 
earth in relatively small proportions and kept aerated 
by occasional mixing undergoes a very thorough decom- 



THE NITROGEN CYCLE 



451 



position of the manure but without any corresponding 
increase in nitrates. On the other hand, under field con- 
ditions, manure used in relatively small amounts does 
not undergo this serious loss. 

The application of twenty tons of farm manure to the 
acre to sod on a clay loam soil for three consecutive years, 
at Cornell University, resulted in a larger production 
of nitrates on the manured soil than on a contiguous plat 
of similar soil left unmanured. This was true during the 
third year of the applications, when the land was in sod, 
and also during the fourth year, when no manure was 
applied to either plat and when both plats were planted 
to corn, as may be seen from the following table : — 



Nitrates Produced on Heavily Manured and on Un- 
manured Soil 



Land in timothy 

April 23 . . 

May 3 . . . 

May 14 . . 

May 30 . . 

June 1 . . . 

June 13 . 

June 20 . . 

July 24 . . 

August 14 . 
Land in maize 

May 19 . . 

June 22 . . 

July 6 . . . 

July 28 . . 

August 10 



NOa IN Parts to a Million, 
Dry Soil 


Unmanured 

30il 


Twenty tons 
manure to the 
acre for three 




years 


8.2 


21.0 


4.1 


4.6 


3.3 


4.5 


2.0 


4.0 


2.4 


2.0 


0.8 


1.1 


1.3 


3.0 


2.2 


2.8 


1.8 


3.0 


17.5 


20.1 


42.8 


79.3 


50.0 


105.0 


195.0 


304.0 


151.0 


184.0 



452 SOILS: PROPERTIES AND MANAGEMENT 

370. Effect of soil aeration on nitrification. — Probably 
the most potent factor governing nitrification in the soil 
is the supply of air. In clay, and even in loam soils, the 
tendency to compactness is such as to prevent the pres- 
ence of sufficient air to enable nitrification to proceed 
as rapidly as desirable unless the soil is well tilled. Col- 
umns of soil eight inches in diameter and eight inches in 
depth were removed from a field of clay loam on the Cor- 
nell University farm, and carried to the greenhouse with- 
out disturbing the structure of the soil as it existed in 
the field. At the same time, vessels of similar size were 
filled with soil dug from a spot near by. These may be 
termed unaerated and aerated soils. Both were kept 
at the same temperature and moisture content in the 
greenhouse, but no plants were grown on them. The 
production of nitrates was as follows : — 



Time op Analysis 


Nitrates in Dry Soil, Parts 
TO THE Million- 


Unaerated soil 


Aerated soil 


When taken from field 

After standing one month .... 
After standing two months .... 


3.2 

4.2 
9.0 


3.2 

17.6 
45.6 



371. Efifect of sod on nitrification. — Nitrification 
proceeds slowly on sod land, especially if the soil is heavy. 
On the same type of soil as that used in the experiment 
last described, the average quantities of nitrates for each 
month of the growing season in the surface eight inches 
of sod land, as compared with maize land under the same 
manuring, were as follows : — 



THE NITROGEN CYCLE 



453 





Month 


Nitrates in Dry Soil, Parts 
TO the Million 




Sod land 


Maize land 


April 

May 


8.9 
3.0 
2.4 
4.0 
5.4 


17 1 


June 


40 3 


July 


194 


August 


186 7 







The amount of nitrogen removed by the maize crop 
was greater than that removed by the timothy; conse- 
quently the greater amount in the former soil cannot be 
due to the effect of the crop. 

So far as the conservation of nitrogen is concerned, 
sod is an ideal crop, for nitrates are formed very little 
faster than they are used, and are not carried off in large 
quantities by the drainage water. 

In' the corn land as much as 175 pounds of nitrate 
nitrogen was present in the first twelve inches of one 
acre, or fully three times as much as was used by the 
crop. 

372. Depths at which nitrification takes place. — War- 
ington ^ concluded from his experiments that nitrification 
takes place only in the surface six feet of soil. Hall ^ 
has pointed to the fact that no more nitrates were leached 
from the 60-inch lysimeter at Rothamsted than from the 
one 40 inches deep ; which is very good evidence that in 



1 Warington, R. On the Distribution of the Nitrifying 
Organism in the Soil. Trans. Chem. Soe., Vol. 51, p. 118. 
1887. 

^ Hall, A. D. The Book of the Rothamsted Experiments, 
p. 230. New York, 1905. 



45-t SOILS: PROPERTIES AND MANAGEMENT 

that particular soil nitrification does not take place below 
40 inches from the surface. In more porous soils, how- 
ever, nitrification probably extends deeper, especially 
in the rich and porous subsoils of arid and semiarid regions. 

In all probability, nitrification is largely confined to 
the furrow slice, where the opening-up of the soil by til- 
lage has provided the necessary air, and where the tem- 
perature rises to a point more favorable to the action 
of nitrifying bacteria. The results from the aerated and 
unaerated soils as shown above represent the differences 
that doubtless exist between the furrow slice and the sub- 
soil so far as nitrification is concerned. 

373. Loss of nitrates from the soil. — Nitrogen hav- 
ing been converted into the form of nitric acid, it im- 
mediately combines with available bases in the soil, 
forming salts, all of which are very easily soluble and 
which are carried in solution by the soil water. In a 
region of much rainfall, the removal of nitrates in the 
drainage water is very rapid. Hall ^ states that nitrates 
formed during the summer or the autumn of one year are 
practically all removed from the soil of the Rothamsted 
fields before the crops of the following year have advanced 
sufficiently to utilize them. It was formerly customary 
to fertilize with ammonium salts in autumn, but the 
drainage water showed on analysis such a large quantity 
of nitrates during the months intervening between the 
time of fertilizing and the opening of the growing season 
that the practice was discontinued. 

In regions of less rainfall or of greater surface evapora- 
tion, the loss in this way is less, reaching a minimum in an 
arid region when irrigation is not practiced. Under 

1 Hall, A. D. The Soil, p. 176. New York, 1903. 



THE NITROGEN CYCLE 455 

such conditions, there is a return of nitrates to the upper 
soil as ca])illary water moves upward to replace evapo- 
rated water. In fact, wherever evaporation takes place 
to any considerable extent there is some movement of 
this kind. The need for catch crops to take up and pre- 
serve nitrogen is therefore greater in a humid region than 
in an arid or a semiarid one. A system of cropping that 
allows the land to stand idle for some time, or a crop that 
requires intertillage, as does maize, fails to utilize all the 
nitrates produced, and promotes the loss of nitrogen in 
drainage water. 

374. Nitrate reduction. — The nitrogen-transforming 
bacteria thus far studied have been those that cause 
the oxidation of nitrogen as the result of their activi- 
ties. A number of forms of bacteria that accomplish a 
reverse action may now be considered. The several 
processes involved are commonly designated by the 
general term denitrifi cation, and comprise the follow- 
ing : 1 , reduction of nitrates to nitrites and ammonia ; 
2, reduction of nitrates to nitrites, and of these to ele- 
mentary nitrogen. 

The number of organisms that possess the ability to 
accomplish one or more of these processes is very large — 
in fact, greater than the number involved in the oxida- 
tion processes ; but, in spite of their numbers, permanent 
loss of nitrogen in ordinary arable soils is unimportant 
in amount, although in heaps of barnyard manure it 
may be a very serious cause of loss. 

Some of the specific bacteria reported as bringing about 
nitrate reduction are : B. ramosus and B. pestifer, which 
reduce nitrates ; B. mycoides, B. sybtilis, B. mesentericiis 
vulgatus, and many other ammonification bacteria which 
are capable of converting nitrates into ammonia. 



456 SOILS: PROPERTIES AND MANAGEMENT 

B. deiiitrificans alpha and B. denitrificans beta reduce 
nitrates with the evohition of gaseous nitrogen. 

375. Nitrate-assimilating organisms. — In addition to 
the nitrate-reducing bacteria already mentioned, there are 
other bacteria which also utilize nitrates ; but, like higher 
plants, these convert the nitrogen into organic nitrog- 
enous substances. However, as they operate in the 
dark and cannot obtain energy from sunlight, they must 
have organic acids or carbohydrates as a source of energy. 
While these bacteria cannot be considered as nitrate 
reducers, they help to deplete the supply of nitrates when 
conditions are favorable for their development. What 
these conditions are is not well understood, nor can any 
estimate be made as to the extent of their operations. 

376. Denitrification. — The term denitrification may 
be used to include both the process of nitrate reduction 
and that of nitrate assimilation (see Fig. 61). 

Most of the denitrifying bacteria perform their func- 
tions only under a limited amount of oxygen, while others 
can operate in the presence of a more liberal supply ; 
but, in general, thorough aeration of the soil practically 
prevents denitrification. Straw apparently carries an 
abundant supply of denitrifying organisms, and also 
furnishes a supply of carbohydrates which favor their 
action ; so that stable manure is very likely to undergo 
denitrification, and straw or coarse stable manure are 
conducive to the growth of denitrifying bacteria in the soil. 

Under ordinary farm conditions, denitrification is 
of no significance in the soil where proper drainage and 
good tillage are practiced. Warington ^ showed that if 

' Warington, R. Investigations at Rothamsted Experi- 
mental Station. U. S. D. A., Office of Exp. Sta., Bui. 8, p. 64. 
1892. 



THE NITROGJSN CYCLE 457 

an arable soil is kept saturated with water to the exclu- 
sion of air, nitrates added to the soil are decomposed, 
with the evolution of nitrogen gas. As lack of drainage 
is usually most pronounced in early spring, when the soil 
is likely to be depleted of nitrates, it is not likely that 
much loss arises in this way unless a nitrate fertilizer has 
been added. Among the many difficulties arising from 
poor drainage, denitrification of an expensive fertilizer 
may be a very considerable item. 

The addition of a nitrate fertilizer to a well-drained soil 
receiving stable manure is not likely to result in a loss of ni- 
trates unless the dressings of manure have been extremely 
heavy. Hall ^ states that at Rothamsted, where large quan- 
tities of nitrate of soda are used every year in connection 
with annual dressings of farm manure, the nitrate produces 
nearly as large an increase when added to the manured 
as when added to the unmanured plat. In other words, 
there appears to be no loss of nitrate by denitrification. 

It is possible to reach a point in manuring at which 
denitrification may take place. j\Iarket-gardeners some- 
times reach this point, when fifty tons or more of farm 
manure, in addition to a nitrate fertilizer, are added to 
the soil. Plowing under heavy crops of green manure 
may produce the same result. In either case, the best 
way to overcome the difficulty is to allow the organic 
matter to partly decompose before adding the fertilizer. 
The removal of the easily decomposable carbohydrates 
needed by the denitrifying organisms decreases or pre- 
cludes their activity. 

377. Nitrogen fixation through symbiosis with higher 
plants. — It has long been recognized by farmers that 

• Hall, A. D. The Book of the Rothamsted Experiments, 
pp. 114-115. New York, 1905. 



^:^ 



458 SOILS: PROPERTIES AND MANAGEMENT 

certain crops, as clover, alfalfa, peas, beans, and some 
others, improve the soil, making it possible to grow larger 
crops of cereals after these crops have been on the land. 
Within the past century the benefit has been traced to 
an increase in the nitrogen content of the soil, and the 
specific plants so affecting the soil were found to be, with 
a few exceptions, those belonging to the family of legumes. 
It has furthermore been demonstrated that under certain 
conditions these plants utilize the uncombined nitrogen of 
the atmosphere (see Fig. 61), and that they contain, 
both in the aerial portions and in the roots, a very high 
percentage of nitrogen. In consequence, the decomposi- 
tion of even the roots of the plants in the soil leaves a 
large amount of nitrogenous matter. 

378. Relation of bacteria to nodules on roots. — It has 
also been shown that the utilization of atmospheric nitro- 
gen is accomplished through the aid of certain bacteria 
that live in nodules (tubercles) on the roots of the plants. 
These bacteria take free nitrogen from the air in the soil, 
and the host plant secures it in some form from the bac- 
teria or their products. The presence of a certain species 
of bacteria is necessary for the formation of tubercles. 
Leguminous plants grown in cultures or in soil not con- 
taining the necessary bacteria do not form nodules and do 
not utilize atmospheric nitrogen, the result being that 
the crop produced is less in amount and the percentage 
of nitrogen in the crop is less than if nodules were formed. 

The nodules are not normally a part of leguminous 
plants, but are evidently caused by some irritation of the 
root surface, much as a gall is caused to develop on a leaf 
or a branch of a tree by an insect. In a culture contain- 
ing the proper bacteria, the prick of a needle on the root 
surface will cause a nodule to form in the course of a few 



THE NITROGEN CYCLE 459 

days. The entrance of the organism is effected through 
a root-hair which it penetrates, and it may be seen as a 
filament extending the entire length of the hair and into 
the cells of the cortex of the root, where the growth of 
the tubercle starts. 

Even where the causative bacteria occur in cultures 
or in the soil, a leguminous plant may not secure any 
atmospheric nitrogen, or perhaps only a small quantity, 
if there is an abundant supply of readily available com- 
bined nitrogen on which the plant may draw. The bac- 
teria have the ability to utilize combined nitrogen as 
well as uncombined nitrogen, and prefer to have it in 
the former condition. On soils rich in nitrogen, legumes 
ma}' therefore add little or no nitrogen to the soil ; while 
in properly inoculated soils deficient in nitrogen an impor- 
tant gain of nitrogen results. 

While B. radicicola is considered the organism common 
to all leguminous plants, it is now known that the organ- 
isms from one species of legume are not equally well adapted 
to the production of tubercles on each of the other species 
of legumes. They show greater activity on some species 
than on others, but do not develop so successfully on all 
species as on the one from which the organisms were 
taken. It was rather generally believed at one time that 
the longer any species of legume is in contact with the 
organisms from another species, the more active this 
species becomes and the greater is the utilization of 
atmospheric nitrogen. Considerable doubt has been cast 
on this view in recent years, and it is now generally con- 
ceded that the bacteria of certain legumes are not capable 
of inoculating certain other species of legumes. 

379. Transfer of nitrogen to the plant. — It has been 
shown by several investigators that bacteria from the 



460 SOILS: PROPEHTIES AND MANAGEMENT 

nodules of legumes are able to fix atmospheric nitrogen 
even when not associated with leguminous plants. There 
would seem to be no doubt, therefore, that the fixation of 
nitrogen in the tubercles of legumes is accomplished di- 
rectly by this organism, not by the plant itself nor through 
any combination of the plant and the organism — though 
both of these hypotheses have been advanced. The part 
played by the plant is doubtless to furnish the carbohydrates 
which are required in large quantities by all nitrogen-fixing 
organisms and which the legumes are able to supply in 
large amounts. The utilization of large quantities of 
carbohydrates by the nitrogen-fixing bacteria in the tuber- 
cles may also account for the small proportion of non- 
nitrogenous organic matter in the plants. 

How the plant absorbs this nitrogen after it has been 
secured by the bacteria is less well understood. Early 
in the growth of the tubercle, a mucilaginous substance 
is produced, which permeates the tissues of the plant in 
the form of long, slender threads containing the bacteria. 
These threads develop by branching or budding, and form 
what have been called Y and T forms, known as bac- 
teroids, which are peculiar to these bacteria. The threads 
finally disappear, and the bacteria diffuse themselves more 
or less through the tissues of the root. ^Yhat part the 
bacteroids play in the transfer of nitrogen is not known. 
It has been suggested that in this form the nitrogen is 
absorbed by the tissues of the plant. It seems quite likely 
that the nitrogen compounds produced within the bacteria 
cells are dift'used through the cell wall and absorbed by 
the plant. 

380. Soil inoculation for legumes. — Immediately fol- 
lowing the discovery of the nitrogen-fixing bacteria, the 
possibility was conceived of securing a better growth of 



THE NITROGEN CYCLE 461 

leguminous crops on soils not having previously grown 
such crops successfully. Extensive experiments showed 
the practicability of inoculating land for a certain legumi- 
nous crop by spreading on its surface soil from a field 
on which the same crop is successfully growing. It is 
manifestly much better to apply the organisms from a 
certain species of legumes from a field having grown the 
same species, than to attempt to use organisms from an- 
other species of legumes. The fact that soil inoculation 
by means of soil from other fields may possibly transmit 
weed seeds and fungous diseases, and also necessitates 
the transportation of a great bulk and weight of material, 
has led to numerous eflForts to inoculate soil by means 
of pure cultures. The pure culture may also make it 
possible to bring to the soil bacteria of greater physio- 
logical efficiency than those already there. 

The first attempt at inoculation by pure cultures 
was made in Germany, the cultures being sold under the 
name of " nitragin." Careful experiments made with 
this material previous to the year 1900 did not show 
it to be very efficient ; but in recent years improvements 
in the method of manipulating the cultures have resulted 
in much greater success. In " nitragin " the medium 
used for growing the organisms is gelatin, and before use 
this was formerly dissolved in water ; but now a solution 
of greater density is used in order to prevent a change of 
osmotic pressure, which may cause plasmolysis and result 
in the destruction of the bacteria. 

Within recent years a number of cultures for soil 
inoculation have been offered to the public. The first 
of these utilized absorbent cotton to transmit the bac- 
teria in a dry state from the pure culture in the laboratory 
to the user of the culture, who was to prepare therefrom 



462 SOILS: PROPERTIES AND MANAGEMENT 

another culture to be used for inoculating the soil. Care- 
ful investigation of this method showed that its weakness 
lay in drying the cultures on the absorbent cotton, which 
frequently resulted in the death of the organisms. More 
recently, liquid cultures have been placed on the market 
in this country, and these have, in the main, proved to 
be more successful, notably those sent out by the United 
States Department of Agriculture. Another very suc- 
cessful culture medium, now being distributed by the 
Department of Plant Physiology at Cornell University, is 
steamed soil. The process of steaming under a pressure 
of two or three atmospheres increases greatly the solu- 
bility of both organic and inorganic matter, and produces 
a medium highly fa\'orable to the development of the 
organisms isolated from the nodules of legumes. 

Liquid cultures for legume inoculation have now been 
prepared and distributed by the United States Depart- 
ment of Agriculture for seven years, and during this time 
a record has been kept of the results so far as it has been 
possible to do this. These are sinnmarized by Keller- 
man ^ as follows : average percentage of success, 70 ; 
average percentage of failure, 24. If, however, the doubt- 
ful reports are included with the failures, the percentage 
of success is reduced to 3S. Kellerman states as his 
opinion that inoculation with pure liquid cultures is as 
certain a means of infection as is inoculation with soil 
from fields on which legumes have been successfnlly grown 
for extended periods, if the soil to be infected is one well 
adapted to the leguminous crop ; but on soils not well 
suited to legumes, the use of soil from old fields is a much 
more satisfactory medium with which to attempt inocula- 

' Kellerman, K. F. The Present Status of Soil Inoculation. 
Centrlb. f. Bakt., II, Band 34, Seite 42-50. 1912. 



THE NITROGEN CYCLE 463 

tion. It is only a question of time until a successful 
method of inoculating soil from artificial cultures will be 
found. In the meantime, inoculation by means of in- 
fested soil is the most practical method. 

381. Nitrogen fixation without symbiosis with higher 
plants. — If a soil is allowed to stand idle, either without 
vegetation or in grass, it will, under favorable moisture 
conditions in the northern states, accumulate in one or two 
years an appreciable amount of nitrogen not present at the 
beginning of the period. At the Rothamsted Experiment 
Station, one of the fields in volunteer plants, consisting 
mainly of grass without legumes, gained in the course of 
twenty years about twenty-five pounds of nitrogen per 
acre annually.^ According to Hall, the nitrogen brought 
down by rain would account for about five pounds to the 
acre per annum, and dust, bird droppings, and the like, for 
a little more. 

382. Nitrogen-fixing organisms. — Direct experiment 
has shown that certain bacteria have the ability to utilize 
atmospheric nitrogen and to leave it in the soil in a com- 
bined form (see Fig. 61). An anaerobic bacillus — Clos- 
tridium pasteurianum — was first found to produce this 
result. Later, a commercial culture called " alinit " was 
placed on the market in Germany, claimed to contain 
Bacterium ellenhachensis, with which the soil was to be 
inoculated, and it was claimed that a large fixation of 
atmospheric nitrogen would result. A number of tests of 
this material failed to show that it caused any marked 
fixation of atmospheric nitrogen. 

A number of other nitrogen-fixing organisms have 
since been discovered. There are : (1) several members 

1 Hall, A. D. On the Accumulation of Fertility by Land 
Allowed to Run Wild. Jour. Agr. Sei., Vol. 1, p. 241. 1905. 



464 SOILS: PliOPEIiTIES AND MANAGEMENT 

of the group designated Azotobacter, which are aerobic 
bacteria, and which some investigators hold to be capable of 
fixing atmospheric nitrogen when grown in pure cultures, 
while others believe them to be able to do so, at least in 
large amounts, only in the presence of certain other 
organisms ; (2) members of the Granulobacter group, 
which are large spore-bearing bacilli of anaerobic habits ; 
(3) Bacillus radiobader, which appear to be closely related 
to or identical with the B. radicicola of legume tubercles. 
The last-named has been shown to be able to fix atmospheric 
nitrogen even when not growing in symbiosis with leg- 
umes. 

There are doubtless many other nitrogen-fixing or- 
ganisms still to be discovered. 

A peculiarity of these nitrogen-fixing organisms is 
their use of carbohydrates, which they decompose in 
the process of nitrogen fixation. They secure more 
atmospheric nitrogen when in a nitrogen-free medium. 
The presence of soluble lime or magnesium salts, especially 
carbonates, is necessary for the best performance of the 
nitrogen-fixing function, as is also the presence of a some- 
what easily soluble form of phosphorus. The organisms 
are exceedingly sensitive to an acid condition of the soil. 

383. Mixed cultures of nitrogen-fixing organisms. — 
Mixed cultures of the various organisms mentioned fix 
larger amounts of nitrogen than do the pure cultures 
of any one of them, while some forms are incapable of 
fixing nitrogen in pure cultures. Certain algre, particularly 
the blue-green alga?, aid greatly in promoting growth and 
nitrogen fixation by these organisms. This they probably 
do by producing carbohydrates, which are used by the 
bacteria as a source of energy for nitrogen fixation, the 
bacteria furnishing the algaj with nitrogenous compounds. 



THE NITROGEN CYCLE 465 

To what extent the relation is symbiotic is not known at 
present, but it seems probable that a relation may exist 
similar to that between leguminous plants and the nitrogen- 
gathering bacteria in their nodules. 

384. Nitrogen fixation and denitrification antagonistic. 
— Nitrogen fixation and denitrification are reverse pro- 
cesses. The former is, for most bacteria, favored by 
an abundant supply of air and a moderately high tempera- 
ture. Thus, at 75° F. fixation was rapid, at 59° F. it was 
decreased, and at 44° F. there was no fixation. Denitri- 
fication is favored by a somewhat limited supply of 
oxygen. 

There is no reason to believe that the practical impor- 
tance of nitrogen fixation without legumes is equal, under 
the most favorable conditions, to that with legumes. 
A further knowledge of the organisms effecting fixation 
and of their habits will doubtless make possible a greater 
utilization of their powers to supplement the use of leg- 
umes as a source of combined nitrogen in the soil. 

TREATMENT OF SOILS W^TH VOLATILE ANTISEPTICS AND 
WITH HEAT 

Attention was first drawn to the effects of carbon bisul- 
fide on the soil in a paper by Girard ^ and one by Oberlin^ 
which appeared in 1894. Girard noticed that soil treated 
with carbon bisulfide for the purpose of combating a para- 
sitic disease of sugar-beet was more productive than it 

1 Girard, A. Reeherehes sur 1' Augmentation des Recoltes 
par rinjection dans le Sol du Sulfure de Carbone a Doses Mas- 
sives. Bui. Soc. Nationale d'Agric, Tome 54, p. 356. 1894. 

^ Oberlin. Bodenmiidigkeit und Schwefelkohlenstoff. Mainz, 
1894. 

2h 



46G SOILS: PROPERTIES AND MANAGEMENT 

was before such treatment. The beneficial effect of the 
treatment extended to the second year. 

Oberhn found a somewliat siniihir condition where 
the soil of vineyards treated witli carbon bisulfide to kill 
phylloxera showed greatly increased productiveness after 
the treatment. The effect of carbon bisulfide on the 
vineyard soil was to make it possible to raise grapes con- 
tinually on the same land, whereas it had previously been 
necessary to rest the land by growing a succession of 
otlier crops at intervals of several years. It was noticed, 
however, that immediately after treatment the plants did 
not grow so well as under normal conditions. Systematic 
investigations of the subject then began, and as early as 
1895 Pagnoul ^ reported that when carbon bisulfide is 
applied to soils nitrification is temporarily depressed. 

Investigation of the effect of heat on soil had begun 
somewhat earlier, when Frank - showed in 1888 that it 
increases the quantities of soluble matter, both organic 
and inorganic, as well as causing the soil to be more pro- 
ductive. 

The subject has been investigated by a large number of 
persons, and in addition to carbon bisulfide a considerable 
number of other volatile antiseptics, including ether, 
chloroform, and toluene, have been found to influence the 
productiveness of soils. The effect of heat, particularly 
in steam, at various temperatures from slightly above 
normal to more than 200° C, has also been studied, wliile 

1 Pagnoul, M. Nouvelles Reeherches sur les Transforma- 
tions que Subit I'Azote dans le Sol. Annales Agronomique, 
Tome 21, pp. 497-501. 189.5. 

^ Frank, B. Ueber den Einfluss welchen das Sterilisiren 
des Erdbodens auf die Pflanzen Entwickelung ausiibt. Ber. 
d. Deut. Bot. Gesell. (Generalversammlungs Heft) Band 4, 
Seite 87-97. 1888. 



THE NITROGEN CYCLE 467 

it has been found that the mere drying of soils effects 
important changes in their solubiHty and in the bacterial 
processes that occur in them. As the result of the in- 
vestigations, certain well-established facts have been 
worked out in connection with certain treatments when 
applied to most soils. 

385. Effects of carbon bisulfide and heat on properties 
of soils. — \'olatile antiseptics usually increase the pro- 
ductiveness of soils, although there may be at first a slight 
temporary retardation of plant growth. It is of course 
customary to permit the antiseptic to volatilize from 
the soil before seed is planted. For this purpose the soil 
is spread out in a thin layer, in which condition it is al- 
lowed to remain until the odor of the antiseptic has dis- 
appeared. The soil is then placed in vessels and moistened 
and the seeds are planted in it. 

Other characteristic effects of treatment with volatile 
antiseptics reported by different investigators are : (1) 
an initial decrease in the numbers of bacteria, followed by 
a long-continued increase ; (2) a disturbance of the equi- 
librium of the bacteria, by which certain types multiply 
more rapidly than others ; (3) a slight initial increase 
in ammonia content, followed by a considerable increase 
in the rate of production of ammonia ; (4) depression of 
the process by which ammonia is converted into nitric 
acid, and a very slow recovery in the activity of the bac- 
teria concerned, as a result of which ammonia accumulates 
in the soil ; (5) an increase in the rate at which oxidation 
takes place in soils ; (6) destruction of protozoa. 

386. Hypotheses to account for effects of carbon 
bisulfide and of heat. — A number of hypotheses have 
been fornuilated by which to Recount for the increased 
plant growth and for changes induced in soils by treat- 



468 SOILS: PROPERTIES AND MANAGEMENT 

ment with heat and volatile antiseptics. A number of 
these theories will be mentioned, but it should be remem- 
bered that much important work on the subject has been 
done by investigators who have not advanced an}- hy- 
potheses. 

387. Koch's theory. — Koch ^ was the first to offer 
any explanation. In 1899 he stated it as his opinion that 
carbon bisulfide has a directly stimulating action on the 
plants themselves. He later ^ found ether to ha^'e a 
similar action, and continued his experiments with carbon 
bisulfide. He found that soil sterilized with heat pro- 
duced better crops when treated with carbon bisulfide 
than when not so treated, and concludes that the effect 
of the antiseptic, therefore, cannot be due to the effect 
of the antiseptic on bacteria. He also experimented with 
field soils, and showed that the size of the crop on treated 
soils is not proportional to the quantity of nitrogen 
contained. 

The theory of Koch has been supported by Fred,^ who 
fertilized soils with an abundant supply of sodium nitrate 
and found that in every case in which carbon bisulfide 
was added the growth and yield of crop were much su- 
perior to those in the corresponding pots not treated with 
that substance. He concludes that as there was no lack 
of plant-food and other conditions favorable to plant 

' Koch, A. Untersuehungen iibcr die Ursaehen der Riibon- 
miidigkeit mit Besonderes R(>ru('ksiehtigung der Sehwefel- 
kohlenstoffbehandlung. Arb. Deut. Landw. Gesell., Heft 40, 
Seite 7-38. 1899. 

- Koch, A. Ueber die Wirkung von Aether Sehwefelkoh- 
lenstoff auf Hohere und Niedere Pflanzen. Centrlb. f. Bakt., 
II, Band 31, Seite 175-185. 1911-1912. 

3 Fred, E. B. Effect of Fresh and Well-rotted Manure 
on Plant Growth. Virginia Poly. Inst. Agr. E.xp. Sta., Ann. 
Rept. 1909-1910, pp. 142-159. 



THE NITROGEN CYCLE 469 

growth, the effect of the antiseptic must have been directly 
on the plants. 

388. Hiltner and Stormer's theory. — According to 
Hiltner and Stormer/ the effect of treatment with carbon 
bisulfide is to cause a disturbance in the equilibrium of 
the different forms of soil bacteria. These investigators 
compared the numbers in three groups of bacteria that 
developed on gelatin plates inoculated from soil infu- 
sions. The groups were Streptothrix, liquefiers, and 
non-liquefiers. The normal relation of these in the soil 
with which they worked was 20 per cent Streptothrix, 
5 per cent liquefiers, and 70 per cent non-liquefiers. After 
treatment with carbon bisulfide the relative proportions 
were 5 per cent, 10 per cent, and 85 per cent, respectively. 
From 70 to 75 per cent of the whole number of bacteria 
were destroyed by the treatment, but the numbers rapidly 
increased after treatment, rising in a few weeks to 50,- 
000,000 to a gram in a soil that contained 10,000,000 to a 
gram before treatment. This increase is due largely to 
the development of the non-liquefiers, the Streptothrix 
remaining at about the same actual number. 

The fact that the equilibrium of the bacterial flora 
was so greatly disturbed by the treatment with carbon 
bisulfide led Hiltner and Stormer to believe that the greater 
productiveness of the soil after treatment is due to the 
greater effectiveness of the surviving and rapidly develop- 
ing forms in rendering available the supply of plant 

1 Hiltner, L., and Stormer, K. Studien iiber die Bakteri- 
enflora des Ackerbodens, mit besonderer Beriieksielitigung 
ihres Verbal tens nach einer Behandlimg mit Schwefelkohlenstoff 
und nacb Braehe. Arb. Biol. Abt. f. Land- u. Forstwirtsehaft 
am Kaiserl. Ges. Arat., Band III. Heft 5. Berlin, 1903. Ab- 
stract in Centrlb. f. Agrikultur Chemie, 33 Jahrg., Seite 361- 
374. 1904. 



470 SOILS: PROPERTIES AND MANAGEMENT 

nutrients in the soil, and to a decrease in the number of 
denitrifying bacteria, which obviates loss of available 
nitrogen through their action. 

Heinze/ working with soils treated with carbon bisul- 
fide, and PfeifFer, Frank, Fricdlander, and Ehrenberg,^ 
working with steamed soils, found that there was a large 
fixation of nitrogen following these treatments. They 
conclude that this is at least partly responsible for the 
greater productiveness of the soils after the treatments 
mentioned. 

389. Russell and Hutchinson's theory. — The next 
comprehensive theory to be brought forward was one by 
Russell and Hutchinson, who account for the increased 
productiveness of soils partially sterilized, either by heat 
or by volatile antiseptics, as due to the use by plants of 
the ammonia, which, as had been shown by previous 
investigators, accumulated in soils so treated by reason 
of the stimulation given to the process of ammonification 
and the depression of nitrification. They hold, further- 
more, that the stimulation of ammonification is brought 
about by the greatly increased numbers of bacteria in 
the soil following the destruction of some larger organisms, 
probably protozoa or allied forms, that normally interfere 
with the activities of tlie ammonifying bacteria. Care- 
ful experiments by these investigators have shown that 
there is a much larger quantity of nitrogen in the combined 
forms of ammonia and nitrates in partially sterilized 

1 Heinze, B. Eine Weitere Mitteilungen iiber den Schwefel- 
kohlenstoff und die CSo-Behandlung des Bodeas. Centrlb. 
f. Bakt., II, Band 18, Seite 56-74, 246-264, 462^70, 624-634, 
790-798. 1907. 

2 Pfeiffer, Th., Frank, L., Friedlander, K., and Ehrenberg, 
P. Der Stickstol'fhaushalt dos Aekerbodens. Mitt. d. Landw. 
Inst. d. Konigl. Univ. Breslau, Band 4, Seite 710-851. 1909. 



THE NITROGEN CYCLE 471 

soils than in untreated soils. There can be no doubt, 
therefore, that, at least for some higher plants, the quan- 
tity of available nitrogen is greater in the treated soils. 

The relation of protozoa to the ammonifying bacteria 
is somewhat more difficult of demonstration. Methods 
for the enumeration of protozoa in the soil are not suffi- 
ciently well worked out to admit of an entirely satisfactory 
study of their relation to the ammonifying bacteria. 
However, Russell and Hutchinson do not hold that pro- 
tozoa are necessarily the limiting factor in ammonia 
production in normal soils, but grant that some other 
organism of comparatively large size may be responsible 
for this. They intimate also that not only the available 
nitrogen, but also the quantities of other plant nutrients, 
are limited by organisms destroyed by partial steriliza- 
tion ; otherwise increased productiveness induced by 
partial sterilization would be confined to soils in which 
nitrogen is normally the limiting factor. The theory 
does imply, however, that plant-food is the limiting factor 
in all soils benefited by partial sterilization imder the 
conditions of the experiment.^ 

1 Russell, E. J., and Darbishire, F. V. Oxidation in soils 
and its relation to productiveness. Part 2. The influence 
of partial sterilization. Jour. Agr. Sci., Vol. 2, pp. 305-326. 
1907. 

Russell, E. J., and Hutchinson, H. B. The effect of partial 
sterilization of soil on the production of plant food. Jour. 
Agr. Sci., Vol. 3, pp. 111-144. 1909. 

Russell, E. J., and Hutchinson, H. B. The effect of partial 
sterilization of soil on the production of plant food. Part 2. 

Russell, E. J., and Hutchinson, H. B. The limitation of bac- 
terial numbers in normal soils and its consequences. Jour. Agr. 
Sci., Vol. 5, pp. 152-221. 1903. 

Buddin, W. Partial sterilization of soil by volatile and 
non-volatile antiseptics. Jour. Agr. Sci., Vol. 6, pp. 417-451. 
1914. 



472 SOILS: PEOPERTIES AND MANAGEMENT 



Some typical results of investigations by Russell and 
Hutchinson on the effect of partial sterilization on bac- 
teria numbers, ammonia production, and presence of 
protozoa are given below : — 





Bacteria 
AFTER Sixty- 


Nitrogen 
as NHa AND 

NOa AFTER 


Detri- 






eight Days, 

TO A Gram op 

Dry' Soil 


Sixty-eight 
Days, Parts 
TO A Million 
OP Dry Soil 


mental 
Factor 


Found 










[Ciliates 


Untreated soil . . 


11,100,000 


13.0 


Present 


< Amoeba 
[ Monads 


Soil heated to 40° C.l 
for three hours J 


7,500,000 


14.4 


Present 


[ Ciliates 
I Amoeba 
[Monads 


Soil heated to 56° C.l 
for three hours J 


37,500,000 


36.7 


Killed 


All killed 



390. Greig-Smith's theory. — An entirely different 
explanation of the effect of partial sterilization on soils 
has been advanced by Greig-Smith.^ He states that 
when disinfectants are applied to the soil their action is 
a double one. They kill the less resistant bacteria, and 
dissolve from the surfaces of the soil particles a waxy 
covering, to which he has given the name " agricere." 
The surviving bacteria, among which are the beneficial 
ones, are able to develop more rapidly because of the 
greater accessibility of the food sui)ply which the re- 
moval of the " agricere " has exposed. 

Greig-Smith holds that heat destroys substances toxic 

' Greig-Smith, R. The BaeteriotO-xins and the "Agrieere" 
of Soils. Centrlb. f. Bakt., II, Band 30, Seite 154-150. 1911. 



THE NITROGEN CYCLE 



473 



to bacteria, and also certain of the less resistant bacteria, 
thus permitting the more resistant species to multiply 
very rapidly owing to the absence of the bacteriotoxins. 

In order to ascertain whether chloroform has any effect 
other than the destruction of protozoa, Greig-Smith 
applied it to soil previously heated to 62° C. (which he 
had found was sufficient to kill all protozoa), and then 
determined the number of bacteria in untreated soil, in 
heated soil, and in soil heated and treated with chloro- 
form. The counts to a gram of soil were made at inter- 
vals, and are shown below : ^ — 





Start 


4 Days 


12 Days 


25 DATS 


39 Days 


Untreated soil 


52 


680,000 


2,700,000 


4,300,000 


5,400,000 


Soil heated 












at 62° C. 


16 


15,800,000 


11,800,000 


9,000,000 


8,000,000 


Soil heated 












at 62° C. 












and treated 












with chlo- 












roform 


13 


24,600,000 


45,400,000 


41,600,000 


90,000,000 



Greig-Smith concludes that as the bacteria developed 
more rapidly in the soil treated with chloroform after 
heating than in the soil which was only heated and in 
which the protozoa were presumably dead, the chloro- 
form must have exerted some beneficial effect other than 
the destruction of protozoa, and assumes that this is due 
to the removal of " agricere." 

Partial or complete sterilization of soils has been prac- 

' Greig-Smith, R. Contributions to our Knowledge of Soil 
Fertility. Proe. Linmean Soc. New South Wales, 1912, Part II, 
pp. 238-243. 



474 SOILS: PROPERTIES AND MANAGEMENT 

ticed in greenhouses for a long time, principally for the 
purpose of combating plant diseases. Its value in in- 
creasing productiveness has been a consideration since 
this phase of the subject has been emphasized by investi- 
gations, and the treatment of " sewage-sick " soils has 
been shown by Russell and Golding ^ to be a practical 
matter. It is as a means of studying the principles of 
soil fertility, however, that the investigation of the sub- 
ject of partial sterilization of the soil is of greatest im- 
portance. 

*■ Russell, E. J., and Golding, J. Investigations on "sick- 
ness" in soil. Part 1. "Sewage sickness." Jour. Agr. Sci., 
Vol. 5, pp. 27-47. 1912. 

Russell, E. J., and Golding, J. Investigations on "sickness" 
in soil. Part 2. "Sickness" in glasshouse soils. Jour. Agr. 
Sci., Vol. 5, pp. 8G-111. 1912. 



CHAPTER XXII 
THE SOIL AIR 

The air of the soil is merely a continuation of the 
atmospheric air into the interstitial spaces of the soil, 
when these are not filled with water. As it is more or 
less inclosed by the soil, movement does not take place 
so readily as it does above the surface of the ground and 
hence the soil air is more greatly influenced by its sur- 
roundings than is atmospheric air. This leads to impor- 
tant differences in composition between the atmospheric 
air and soil air, the composition of the latter depending 
on a variety of conditions in which physical, chemical, 
and biological properties play a part. 

FACTORS THAT DETERMINE VOLUME 

The amount of air that soils contain varies with their 
properties, and in any one soil the air content varies with 
certain changes to which the soil is subject from time to 
time. The factors that influence the volume of air in 
soils are : (1) texture; (2) structure ; (3) organic matter ; 
(4) moisture content. 

391. Texture. — The size of the soil particles affects 
the air capacity of the soil in exactly the same way 
as it does the pore space, since in dry soil they are 
identical. A fine-textured soil in a dry condition would 
therefore contain as large a volume of air as would a 

476 



476 SOILS: PROPERTIES AND MANAGEMENT 

coarse-textured soil, provided the particles were spherical 
and all of the same size. Under the conditions actually 
existing in the field, the soils composed of small particles 
generally possess the larger amount of air space. 

392. Structure. — The volume of air in a water-free 
soil being identical with the pore space, the formation 
of aggregates of particles is favorable to a large air volume. 
The volume of air in any soil, therefore, changes from 
time to time ; and particularly is this true of a fine- 
grained soil, in which the changes in structure are greater 
than in a soil with large particles. A change in soil 
structure may greatly alter the volume of air contained 
by changing the pore space, thereby influencing the pro- 
ductiveness. Clay is affected to the greatest extent in 
this way. 

393. Organic matter. — Since organic matter is more 
porous than mineral particles of any size or arrangement, 
the effect of that constituent is always to increase the 
volume of air. While this is generally beneficial in a 
humid region, it is often very injurious in an arid region. 
Unless sufficient water falls on the soil to wash the soil 
particles around the organic matter and to maintain a 
supply sufficient to promote decomposition, the presence 
of vegetable matter leaves the soil so open that the capil- 
lary rise of moisture is interfered with, and the consider- 
able movement of air keeps the soil dry, with the result 
that the portion of the soil layer mixed with and lying 
above the organic matter is too dry to germinate seeds 
or to support plant growth. 

394. Moisture content. — It is quite evident that the 
larger the proportion of the interstitial space filled with 
water, the smaller will be the quantity of air contained. 
This does not necessarily mean that the higher the per- 



THE SOIL AIR 477 

centage of water in the soil, the smaller will be the volume 
of air, since the amount of pore space determines both the 
water and the air capacity. A soil with 30 per cent 
moisture may contain more air than one with a water 
content of 20 per cent, because of the tendency of mois- 
ture to move the soil particles farther apart. 

In soils in the field, the average diameter of the cross 
section of the pore space is the most potent factor in 
determining the volume of air. Small spaces are likely 
to hold water, while larger spaces, not retaining water 
against gravity, are filled with air. 

In a clay soil the volume of air is increased, other 
things being equal, by the formation of granules, and is 
decreased by deflocculation or compaction. The volume 
of air in any soil may be calculated from the following 
formula : — 

% air space = % pore space — (% H2O X ap. sp. gr.) 



COMPOSITION OF SOIL AIR 

The air of the soil differs from that of the outside 
atmosphere in that it contains more water vapor, a much 
larger proportion of carbon dioxide, a correspondingly 
smaller amount of oxygen, and slightly larger quantities 
of other gases, including ammonia, methane, hydrogen 
sulfide, and the like, formed by the decomposition of 
organic matter. 

395. Analyses of soil air. — The composition of the 
air of several soils, as determined by Boussingault and 
Lewy, is quoted by Johnson ^ in the table following : — 

» Johnson, S. W. How Crops Feed, p. 219. New York, 1891. 



478 SOTLS: PROPERTIES AND MANAGEMENT 



Character 
OF Soil 



Volume in One 

Acre of Soil to 

Depth op 14 

Inches 



Air 
(Cu. ft.) 



Carbon 
Dioxide 
(Cu. ft.) 



Composition of 100 Parts 
of Soil Air by Volume 



Carbon 
Dioxide 



Oxygen 



Nitrogen 



Sandy subsoil of forest . 
Loamy subsoil of forest . 
Surface soil of forest . 

Clay soil 

Soil of asparagus bed not 

manured for one year . 
Soil of asparagus bed 

freshly manured 
Sandy soil, six days after 

manuring 

Sandy soil, ten days after 

manuring (three days 

of rain) 

Vegetable mold compost 



4,416 

3,530 

5,891 

10,310 

11,182 

11,182 

11,783 



11,783 
21,049 



14 

28 
57 
71 

86 

172 

257 



1,144 

772 



0.24 
0.79 
0.87 
0.66 

0.74 

1.54 

2.21 



9.74 
3.64 



19.66 
19.61 
19.99 

19.02 

18.80 



10.35 
16.45 



79.55 
79.52 
79.35 

80.24 

79.66 



79.91 
79.91 



There are several factors that influence the composi- 
tion of the soil air, those of greatest importance being 
the production and escape of carbon dioxide. 

396. Sources of carbon dioxide in soil air. — The 
presence of carbon dioxide in soils is due in small part 
to infiltration from the atmospheric air, there being a 
tendency for the carbon dioxide, which is heavier than 
oxygen and nitrogen, to settle out. It may also have a 
purely chemical origin. But in much greater measure 
is the carbon dioxide a product of biological processes 
that occur in the soil. At one time it was believed that 
the formation of carbon dioxide in soils was a purely 
chemical process of oxidation, and possibly a part of the 
gas is formed in that way. It has already been seen that 
there is a condensation of gases in the manifold pores 



THE SOIL AIR 479 

of the soil (see par. 268), the organic portion of which is 
especially capable of condensing gases. Oxygen con- 
densed on the surface of this organic matter would, in 
the words of Johnson,^ " spend itself in chemical action," 
of which carbon dioxide would be the result. 

There is now no doubt, however, that biological pro- 
cesses are largely responsible for the occurrence of the 
large quantity of carbon dioxide in the soil air. There 
are two distinct processes involved : (1) the physiological 
action of bacteria by which they absorb oxygen and give 
off carbon dioxide, and (2) the excretion of carbon dioxide 
by plant roots. The extent to which carbon dioxide is 
produced in normal soils in these two ways has been es- 
timated by Stoklasa,^ who has done much work on the 
subject. He concludes that the microorganisms in 
an acre of soil to a depth of four feet may produce between 
sixty-five and seventy pounds of carbon dioxide a day 
for two hundred days in the year, and that during the 
growing period the roots of oats or wheat would give 
off nearly as much to an acre. 

397. Production of carbon dioxide as affecting com- 
position. — Although the formation of carbon dioxide 
in the soil depends on the decomposition of organic 
matter, it is not always proportional to the quantity 
of organic matter present. The rate of decomposition 
varies greatly, and where this is depressed, as is sometimes 
seen in muck or forest soils, the content of carbon dioxide 
is relatively low. A high percentage of organic matter 



1 Johnson, S. W. How Crops Feed, p. 218. New York, 
1891. 

"^ Stoklasa, J. Ueber den Ursprung die Menge und die 
Bedeutung des Kohlendioxids im Boden. Centrlb. f. Bakt., II, 
Band 14, Seite 723-736. 190-5. 



480 SOILS: PROPERTIES AND MANAGEMENT 

is in itself likely to prevent a proportional formation of 
carbon dioxide, since the accumulation of the gas may 
inhibit further activity of the decomposing organisms. 

Ramann * states that the percentage of carbon dioxide 
in the soil air has the following relations : — 

1. The carbon dioxide increases with the depth. 

2. In general the percentage of carbon dioxide rises 
and falls with the temperature, being higher in the warm 
months and lower in the cold months. 

3. Changes in temperature and air pressure change the 
percentage of carbon dioxide. 

4. In the same soil the content of carbon dioxide varies 
greatly from year to year. 

5. An increase of moisture in the soil increases the per- 
centage of carbon dioxide. 

6. The amount of carbon dioxide varies in different 
parts of the soil. 

The movement of carbon dioxide from the soil depends 
chiefly on diffusion into the outside atmosphere. The 
conditions governing diffusion, which will be discussed 
elsewhere (par. 400), therefore largely determine the 
rate of loss of carbon dioxide from the soil. 

FUNCTIONS OF THE SOIL AIR 

Both oxygen and carbon dioxide, as they exist in the 
air of the soil, have important relations to the processes 
by which the soil is maintained in a habitable condition 
for the roots of plants. Deprived of these gases, the soil 
would soon become sterile. 

398. Oxygen. — An all-important process in the soil 
is that of oxidation, because by it the organic matter 

1 Ramann, E. Bodenkunde. Seite 301. Berlin, 1905. 



THE SOIL AIR 481 

that would soon accumulate to the exclusion of higher 
plant life is disposed of, and the plant-food materials 
are brought into a condition in which they may be ab- 
sorbed by plant roots. The presence of oxygen is essen- 
tial to the life of the decomposing organisms and to the 
complete decay of organic matter. Through this pro- 
cess, roots of past crops, as well as other organic matter 
that has been plowed under, are removed from the soil. 
The process of decay gives rise to products, chiefly car- 
bon dioxide, that are solvents of mineral matter, and leaves 
the nitrogen and ash constituents more or less available 
for plant use. 

Oxygen is also necessary for the germination of seeds 
and the growth of plant roots. These phenomena, al- 
though not involving the removal of large quantities 
of oxygen, are yet entirely dependent on its presence in 
considerable amounts. 

399. Carbon dioxide. — The solvent action of carbon 
dioxide is its most important function in the soil. By 
this action it prepares for absorption by plant roots most 
of the mineral substances found in the soil. Although 
a weak acid when dissolved in water, its universal pres- 
ence and continuous formation during the growing season 
results in a large total effect. 

Carbonic acid dissolves from the soil more or less of 
all the nutrients required by plants. The amounts so 
dissolved are appreciably greater than those dissolved 
in pure water. The constant formation of carbon dioxide 
by decomposition of organic matter keeps this solvent 
continually in contact with the soil. 

Carbon dioxide serves a useful purpose in combining 
with certain bases to form compounds beneficial to the 
soil. Particularly is this the case with calcium carbonate, 
2i 



482 SOILS: PROPERTIES AND MANAGEMENT 

which is of the greatest benefit to the soil in maintaining 
a slight alkalinity very favorable to the development of 
many beneficial bacteria and to the maintenance of good 
tilth. 

Stoklasa ^ has correlated the carbon dioxide production 
with the quantity of phosphates found in the drainage 
water from certain soils. Some of his results are given 
below : — 





P2O6 IN Drainage 

Water 

(Kilograma to a hectare) 


Relative Produc- 
tion OP CO2 
(Milligrams to a kilo- 
gram soil in 24 hours) 


Loam 

Clay 

Lime soil 

Humous soil 


5.2 
3.5 

5.8 
8.4 


24 
15 
36 
56 



Stoklasa considers that the production of carbon dioxide 
is a measure of the intensity of bacterial action in the 
soil, and that in consequence of this activity the phos- 
phorus is rendered soluble. 

When carbon dioxide is combined as sodium carbonate 
or potassium carbonate in considerable quantity, as in 
certain alkali soils, a very injurious action on plant roots 
and on soil structure results. On plants the carbonate 
acts as a direct poison (see par. 305). The effect on 
soil structure is to deflocculate the particles producing 
the separate grain or the compact arrangement (see par. 
420). 



' Stoklasa, .J. Methoden zur Bostimmung dor Atmungs- 
intensitat dor Rakterion iin Roden. Zoit. f. d. I>and\v. Versuchs- 
wesen in Oesterreich, Rand 14, Seite 1243-79. 1911. 



THE SOIL AIR 483 



MOVEMENT OF SOIL AIR 



There is a constant movement of the air in the inter- 
stitial spaces of the soil and an exchange of gases between 
the soil atmosphere and the outside atmosphere, as well 
as a more general, but probably less effective, movement 
of the air out of or into the soil, as the controlling condi- 
tions may determine. The movement may be produced 
by any one or more of the following phenomena: (1) 
diffusion of gases ; (2) movement of water ; (3) changes 
in atmospheric pressure ; (4) changes of temperature in 
atmosphere or in soil ; (5) suction produced by wind. 

400. Diffusion of gases. — The wide difference in the 
composition of soil and atmospheric air gives rise to a 
movement of gases due to a tendency for the external 
and the internal gases to come into equilibrium. Accord- 
ing to Buckingham/ the interchange of atmospheric and 
soil air is due in large measure to diffusion. 

The rate of movement of the soil air due to diffusion 
is dependent on the aggregate volume of the interstitial 
spaces, not on their average size. Thus, it is the porosity 
of the soil that influences most largely the diffusion of 
the air from it. Consequently the size of the particles 
is not a factor, but good tilth permits diffusion to take 
place more rapidly than does a compact condition of soil, 
as the volume of the pore space is thereby increased. 
Compacting the soil in any way, as by rolling or trampling, 
has the opposite effect. 

401. Movement of water. — As water, when present 
in a soil, fills certain of the interstitial spaces, it decreases 
the air space when it enters the soil and increases it when 

1 Buckingham, E. Contributions to Our Knowledge of 
the Aeration of Soils. U. S. D. A., Bur. Soils, Bui. 2-5. 1904. 



484 SOTLS: PROPERTIES AND MANAGEMENT 

it leaves. The downward movement of rain water pro- 
duces a movement of soil air by forcing it out through 
the drainage channel below, while at the same time a 
fresh supply of air is drawn in behind the wave of satura- 
tion as the water passes down from the surface. The 
movement thus occasioned extends to a depth where 
the soil becomes permanently saturated with water. 
Twenty-five per cent of the air in a soil may be driven out 
by a normal change in the moisture content of the soil. 

402. Changes in atmospheric pressure. — Waves of 
high or of low atmospheric i)ressure, frequently involving 
a change of 0.5 inch on the mercury gauge, cross the con- 
tinent alternately every few days. The presence of a 
low pressure allows the soil air to expand and issue from 
the soil, while a high pressure following causes the out- 
side air to enter in order to equalize the pressure. An 
appreciable, but not important, movement of soil air is 
produced in this way. 

The size of the interstitial spaces is more potent than 
their volume in effecting soil ventilation by this and the 
following methods. 

403. Changes of temperature in atmosphere or in soil. — 
A movement of soil air may be induced by a change of 
temperature in the atmosphere or in the soil itself. Changes 
in atmospheric temperature act in the same way as do 
changes in atmospheric pressure ; in fact, it is the effect 
of temperature on air pressure that causes the movement. 
Like the movement due to atmospheric pressure, it is 
not great ; but where the soil immediately at the surface 
of the ground attains a temperature of 120° F. at midday, 
as is the case in the Corn Belt, the movement must be 
appreciable. 

The diurnal change in soil temperature decreases 



THE SOIL AIR 485 

rapidly from the surface downward, due to the absorp- 
tion and slow conduction of heat (see par. 227). At 
the Nebraska Experiment Station ^ the average diurnal 
range for the month of August, 1891, was as follows : — 

Diurnal Range of Air and Soil Temperatures 

Degrees Fahrenheit 

Air 5 feet above ground 14.4 

Soil 1 inch below surface 17.9 

Soil 3 inches below surface 14.8 

Soil 6 inches below surface 9.2 

Soil 9 inches below surface 6.6 

Soil 12 inches below surface 4.3 

Soil 24 inches below surface 0.5 

Soil 36 inches below surface 0.0 

This soil contains about fifty per cent of pore space, in 
the upper foot of which forty per cent is normally filled 
with water during the summer months. This leaves 518 
cubic inches of air in the upper cubic foot of soil. With 
an increase in temperature, the air expands 4^^ in volume 
for each degree Fahrenheit. The average increase of 
temperature is, in this case, about 11 degrees Fahrenheit 
for the first foot. The air exhaled or inhaled by each 
cubic foot of soil would then be 

518 Xll A 1 n !_•• 1- 

=11.6 cubic mches 

491 

As this is slightly over two per cent of the air contained 
in the upper foot of soil, and as the movement below 
that depth is negligible, the change in composition at any 

1 Swezey, G. D. Soil Temperatures at Lincoln, Nebraska. 
Neb. Agr. Exp. Sta., 16th Ann. Kept., pp. 95-102. 1903. 



486 SOILS: PROPERTIES AND MANAGEMENT 

one time is not great ; but this pumping effect is kept up 
day after day, although less energetical 1\' in the cooler 
seasons of the year. In proportion as poor drainage 
equalizes the temperature it would prevent this type of 
circulation. The total eil'ect, assisted by diffusion, is to 
aid materially in ventilating the soil. Owing to ditt'usion 
of air in the interstitial spaces, the air expelled is different 
in composition from that inhaled. 

404. Suction produced by wind. — The mo\ement of 
wind, being almost always in gusts, alternately increases 
and decreases the atmospheric pressure at the surface 
of the soil. There is a tendency, therefore, for the soil 
air to escape and for atmospheric air to penetrate the 
soil with each change in pressure. The effect presumably 
influences only the superficial air spaces, but it must be 
very frequent in its action. No measurements have 
been made and no definite estimate of its effect can be 
stated. 

METHODS FOR MODIFYING THE VOLUME AND THE MOVE- 
MENT OF SOIL AIR 

The conditions that influence the ventilation of soils 
are: (1) volume and size of the interstitial spaces; (2) 
moisture content ; (3) daily and annual range in tem- 
perature. 

Although the size of the interstitial spaces does not 
appear to greatly influence the diffusion of gases from 
a soil, it has a marked effect on certain of the other pro- 
cesses by which air enters and leaves the soil. A sandy 
soil, a soil in good tilth, and, particularly, a soil composed 
of clods, permit of more rapid movement of air than does 
a compact soil. 



THE SOIL AIR 487 

While a certain movement of air through the soil is 
desirable, and indeed necessary, for the reasons already 
stated a very considerable movement is injurious unless 
there is an abundant rainfall. The effect of air move- 
ment through the soil is to remove soil moisture. In a 
region of light rainfall and low atmospheric humidity, this 
may be disastrous if the soil is not kept compact by care- 
ful tillage. On the other hand, in a humid region and 
in clay soil there is likely to be too small a supply of oxygen 
for the use of crops and lower plant life unless the soil 
is well stirred. 

405. Tillage. — The ordinary operations of tillage 
greatly influence the ventilation of the soil. When a soil 
is plowed, the soil at the bottom of the furrow is exposed 
directly to the air at the surface, and, by the separation 
of adhering particles and aggregates of particles, air 
is brought into contact with particles that may previously 
have been completely shut off from air. It is partly 
because of its effect on soil ventilation that plowing is 
beneficial, and the necessity for its practice is greater 
in a humid region and on a heavy soil than in a region 
of light rainfall and on a light soil. The practice of list- 
ing corn, by which the soil is sometimes left unplowed 
for a number of years, although in semiarid regions pro- 
ductive of crops of sufficient yield to make them profitable, 
would fail utterly on the heavy soils of a humid region. 

Subsoiling, by loosening the subsoil, increases the 
ventilation to a greater depth. Rolling and subsurface 
packing both diminish the volume and the movement of 
air. Their essential difference is in their effect on mois- 
ture rather than on air. Harrowing and cultivation have 
the opposite effect, and both increase the production of 
nitrates in the soil by promoting aeration. 



488 SOILS: PROPERTIES AND MANAGEMENT 

406. Manures. — Farm manures, lime, and those 
amendments that improve the structure of the soil, have 
for that reason a beneficial action on soil aeration. By 
their effect on the physical condition of the soil they 
increase its permeability, and by their action in con- 
tributing to the production of carbon dioxide they stimu- 
late diffusion. 

It is chiefly through its effect in increasing the volume 
of air space in soils that farm manure is injurious in light 
soils of semiarid regions. It may thus be injurious in- 
stead of beneficial, if used under certain conditions. 

407. Underdrainage. — By lowering the water table, 
underdrainage by means of tiles remo\'es from the soil 
the water from all but the small capillary spaces, and 
leaves free to the air the remainder of the interstitial 
spaces. There is also a very considerable movement 
of air through the drains, and a movement of air upward 
from the drains to the surface of the soil, which serves 
to aerate to some extent this intervening layer. The 
aeration of the soil brought about by underdrainage 
is one of its beneficial features. 

408. Irrigation. — The influence of irrigation on the 
soil is much like that of rainfall. The alternate filling 
and emptying of the interstitial spaces with water and 
air causes a very considerable change of air. 

409. Cropping. — The roots of plants loft in the soil 
after a crop has been harvested decay and leave channels 
in the soil through which air penetrates. Below the fur- 
row slice, where the soil is not stirred and where it is 
usually more dense than at the surface, this affords an 
important means of aeration. The absorption of moisture 
from the soil by roots also causes the air to penetrate, in 
order to replace the water withdrawn. 



CHAPTER XXIII 
COMMERCIAL FERTILIZERS 

As treated in this volume, manures include all those 
substances, with the exception of water (the function and 
application of which is discussed in par. 167), that are 
added to soils to make them more productive. There are 
several ways in which manures applied to soils may in- 
crease plant growth : (1) by addition of the nutrient mate- 
rials utilized by plants, which is the chief function of 
most of the so-called commercial fertilizers ; (2) by im- 
provement of the physical condition of a soil, which 
usually results from the application of lime and the in- 
corporation of organic matter ; (3) by favoring the action 
of useful bacteria, which is one of the beneficial results 
of farm manure and also of lime ; (4) by counteracting 
the effects of toxic substances — as, for instance, the 
conversion of sodium carbonate into sulfate by gypsum, 
or the neutralization of acidity, or possibly the destruc- 
tion of toxic organic substances by certain salts ; (5) by 
catalytic action, either on chemical processes in the soil 
or by its influence on those bacteria that exert a favorable 
influence on soil fertility or by direct stimulation of the 
plant. 

410. Early ideas of the function of manures. — 
Manures were at one time supposed to pulverize the soil, 
and the French word manoeuvrer, from which the word 
manure comes, implies to work with the hand. This 

489 



490 SOILS: PROPERTIES AND MANAGEMENT 

idea probably originated through the observation that 
farm manure, which was the only manure in use at that 
time, made the soil less cloddy. 

It has been argued, notably by Jethro Tull,^ that since 
tillage pulverizes the soil it may be used as a substitute 
for manures. There are, however, conditions aside from 
tilth that are influenced by manures, and good tilth alone 
will not suffice to maintain a permanently intensive agri- 
culture. It is true in the United States, as it is in Europe, 
that a large consumption of manures goes hand in hand 
with a highly developed and intensive system of farming. 

411. Development of the idea of the nutrient function 
of manures. — While the use of animal excrement on cul- 
tivated soils was practiced as far back as systematic agri- 
culture can be definitely traced, the earliest record of 
the use of mineral salts for increasing the yield of crops 
was published in 1()69 by Sir Kenelm Digby.- He says: 
" By the help of plain salt petre, diluted in water, and 
mingled with some other fit earthly substance, that may 
familiarize it a little with the corn into which I endeavored 
to introduce it, I have made the barrenest ground far 
outgo the richest in giving a prodigiously plentiful har- 
vest." His dissertation does not, however, show any 
true conception of the reason for the increase in the crop 
through the use of this fertilizer. In fact, the want of 
any real knowledge at that time of the composition of 
the plant would have made this impossible. 

In 1804, Theodore de Saussure ^ published his chemical 



1 TuU, Jethro. Horse-Hoeing Husbandry. London. 1829. 

^ Diffby, Kenelm. A Discourse Concerning the Vegetation 
of Plants. London. 16(i9. 

' Saussure, Theodore de. Recherches Chimiques sur la 
Vegetation. Paris. 1804. 



COMMERCIAL FERTILIZERS ' 491 

researches on plants, in which he, for the first time, 
called attention to the significance of the ash ingredients 
of plants, and pointed out that without them plant life 
is impossible and, further, that only the ash of the plant 
tissue is derived from the soil. 

Justus von Liebig,^ in his writings published about 
the middle of the nineteenth century, emphasized still 
more strongly the importance of mineral matter in the 
plant and the extraction of this matter from the soil. 
He refuted the theory, at that time popular, that plants 
absorb their carbon from humus, but he made the mis- 
take of attaching little importance to the presence of 
humus in the soil. He showed the importance of potas- 
sium and phosphorus in manures, but in his later expres- 
sions he failed to appreciate the value of nitrogenous 
manures, holding that a sufficient amount is washed 
from the atmosphere in the form of ammonia. 

A true conception of the necessity for a supply of 
combined nitrogen in the soil was even at that time enter- 
tained by Boussingault and by Sir John Law^es, although 
the elaborate experiments conducted by Lawes, Gilbert, 
and Pugh - in 1857 were required to fully demonstrate 
the fact. Their care in conducting the experiments 
resulted in their sterilizing the soil with which they ex- 
perimented, and hence their failure to discover the utiliza- 
tion of free atmospheric nitrogen by legumes. 

1 Liebig, J. Justus von. Principles of Agricultural Chemistry 
with Special Reference to the Late Researches Made in England. 
London. 1855. Also, Chemistry in its Applications to Agri- 
culture and Physiology. New York. 1556. 

^ Lawes, J. P)., Gilbert, J. IL, and Pugh, E. On the Sources 
of the Nitrogen of Vegetation, with Special Reference to the 
Question whether Plants Assimilate Free or Uncombined Nitro- 
gen. Rotliamsted Memoirs, Vol. 1, No. 1. 1862, 



492 SOILS: PROPERTIES AND MANAGEMENT 

Between 1840 and 1850, Sir John Lawes began the 
manufacture of bone superphosphate, and about the 
same time Peruvian guano and nitrate of soda were intro- 
duced into Euroj)e. The commercial fertilizer industry 
thus dates from that time. 

412. Classes of manures. — While manures are very 
numerous as to kind and while a certain manure may have 
a number of distinct functions, they may yet be roughly 
divided into classes. They will accordingly be treated 
here under the following heads : (1) commercial fertilizers ; 
(2) soil amendments ; (3) farm manures ; (4) green 
manures. 

413. Commercial fertilizers. — Although the commer- 
cial fertilizer industry is little more than half a century 
old, the sale of fertilizers in this country amounts to more 
than §110,000,000 annually. Animal refuse and phos- 
phate fertilizers are exported, while nitrate of soda and 
potassium salts are imported. 

Of the fertilizers sold in the United States in 1909, 
about fifty per cent was consumed in the South Atlantic 
States, in an area lying within three hundred miles of 
the seaboard. Nearly one-half of the remainder was pur- 
chased in the jNIiddle Atlantic and New England States. 
Only five per cent was purchased west of the Mississippi 
River. ^ 

Primarily the function of commercial fertilizers is to 
add plant nutrients to the soil, usually in a form more 
readily soluble than those already present in large quan- 
tity. While other beneficial effects may be produced by 
certain fertilizers, these are usually of secondary impor- 
tance as compared with the addition of the plant nutrients. 

1 Statistics from Thirteenth Census of the United States. 
Abstract of the Census, p. 372. Washington. 1913. 



COMMERCIAL FERTILIZERS 493 

414. Fertilizer constituents. — Prepared fertilizers, as 
found on the market, are usually composed of a number 
of ingredients. Since these are the carriers of the fertiliz- 
ing material, and since it is on their composition and solu- 
bility that the value of a fertilizer depends, a knowledge 
of the properties of these constituents is of interest to 
every one who uses fertilizers and is a valuable aid in their 
purchase. 

FERTILIZERS USED FOR THEIR NITROGEN 

Nitrogen is the most expensive constituent of manures 
and is of great importance, since it is very likely to be 
deficient in soils. A commercial fertilizer may have its 
nitrogen in the form of soluble inorganic salt, or combined 
as organic material. On the form of combination de- 
pends to a certain extent the value of the nitrogen, as 
the soluble inorganic salts are very readily available to 
the plant, while the organic forms must pass through the 
various processes leading to nitrification before the 
plant can use the nitrogen so contained. The inorganic 
nitrogen fertilizers are sodium nitrate, ammonium sulfate, 
calcium nitrate, and calcium cyanamide. 

415. Forms in which nitrogen exists in soils. — There 
are several forms in which nitrogen exists in soils. The 
uncombined nitrogen of the soil air constitutes the largest 
supply because of its diffusibility with the atmospheric 
air. Next in quantity is the nitrogen of organic com- 
pounds, ranging from 0.05 to 0.3 per cent in ordinary 
arable land and slightly, but appreciably, soluble in soil 
water. In upland cultivated soils the nitrogen of nitrate 
salts forms the next largest supply, but rarely exceeds 
20 per cent of the total combined nitrogen of the soil. 



494 SOILS: PROPERTIES AND MANAGEMENT 

In swamp and inundated soils the nitrogen of ammonium 
salts and nitrites forms a larger proportion of the soil 
nitrogen than does the nitrate nitrogen, but in well 
aerated soils these compounds exist in very small quan- 
tities. 

416. Forms in which nitrogen is absorbed by plants. — 
The utilization of atmospheric nitrogen by leguminous 
plants and by a few others that have nodule-bearing roots 
has been established beyond question ; but the extent 
to which this form of nitrogen may be utilized by other 
plants, or the identity of the plants that participate in 
its use, are subjects on which opinions differ, and which 
are still being investigated. 

417. Use of nitrates by plants. — Boussingault first 
demonstratefl the importance of nitrates for higher 
plants. Previous to that time ammonia had been con- 
sidered the chief source of nitrogen, and at a still earlier 
time humus had been considered the source. Liebig 
gave the weight of his influence in favor of ammonia 
as the supply. He was iniaware, of course, of the trans- 
formation of ammonia nitrogen into nitrates in the soil. 
Since the publication of the experiments by Boussin- 
gault and the later work on nitrification, there has 
been a tendency to consider nitrate nitrogen as the 
only available supply of nitrogen for agricultural plants. 
While this is an extreme view of the matter, the 
fact remains that all the higher plants, including the 
legumes, appear to be able to absorb nitrates, and this 
form of nitrogen has frequently proved of greater benefit 
to plants than other forms of nitrogen tested at the 
same time. 

418. Ammonia as a plant-food. — That rice plants on 
swamps use ammonia nitrogen rather than other forms 



COMMERCIAL FERTILIZERS 495 

has been demonstrated by Kellner ^ and later by Kelley.^ 
On upland soils, however, it is presumable that rice plants 
utilize nitrate nitrogen, which would indicate that some 
plants, at least, may adapt themselves to the use of the 
more abundant form of nitrogen. 

Hutchinson and Miller ^ found that peas obtained 
nitrogen from ammonium salts as readily as from sodium 
nitrate, but that wheat plants, although able to obtain 
nitrogen directly from ammonium salts, grew much better 
in a solution containing nitrates. One feature brought 
out by the numerous experiments with ammonium salts 
is the difference between plants of various kinds in respect 
to their ability to absorb nitrogen in this form. 

419. Utilization of humus compounds by plants. — 
One of the early beliefs in regard to plant nutrition was 
that organic matter as such is directly absorbed by higher 
plants. This opinion was afterwards entirely replaced 
by the mineral theory propounded by Liebig ; and still 
later the discovery of the nitrifying process almost dis- 
posed completely of the belief that organic matter is a 
food for higher plants. It is quite certain, however, that 
some organic nitrogenous compounds furnish suitable 
nutrient material for some higher plants without under- 
going bacterial change. 

Hutchinson and Miller, in the paper just referred to, 
give the following list of the organic substances used in 

1 Kellner, O. Agrikulturcheraische Studien iiber die Reis- 
kultur. Landw. Vers. Stat., Band 30, Seite 18-41. 1884. 

^ Kelley, W. P. The Assimilation of Nitrogen by Rice. 
Hawaii Agr. Exp. Sta., Bui. 24, pp. 5-20. 1911. 

3 Hutchinson, H. B., and Miller. N. H. J. The Direct 
Assimilation of Inorganic and Organic Forms of Nitrogen by 
Higher Plants. Centrlb. f. Bakt., II, Band 30, Seite 513-547. 
1911. 



496 SOILS: PROPERTIES AND MANAGEMENT 

experiments by various investigators, and their avail- 
ability for the nutriment of higher plants : — 

Readily Assimilated 

Ammonium salts 
Acetamide CH3 . CO . NH2 

Urea CO\^t.^tt^ 

Barbituric acid (with calcium carbonate) 

/XH . C0\^ 

Alloxan CO<^^.TT ' p^yCO 
Humates 

Assimilated 

Formamide H . CO . XH. 

Glycine XH2 . CHo . COOH 

Aminopropionic acid CH3 . CII(X^H2) . COOH 

/XH 
Guanidine hydrochloride XH . C<^^.tt^ 

Cyanuric acid CO<\^^j^tt po/*^^ 

CO . XH2 

Oxamide | 

CO . XH2 

CH(XH2)C00TI 
Sodium aspartate | 

CH2 . COOH 
Peptone 



COMMERCIAL FERTILIZERS 497 

Doubtful 
Trimethylamine 

para-+Urazine CO\'^tt xttj/^^ 

Hexamethylenetetramine 

Not Assimilated 
Ethyl nitrate Hydroxylamine hydrochloride 

Propionitrile Methyl carbonate 

Toxic 
Tetranitromethane 

Tliis list comprises only those substances that have been 
used in experiments with peas. Many other substances 
remain to be tested, and those already tested may act 
differently with "other plants. 

One of the organic compounds isolated from soils by 
Shorey/ called creatinine, has been shown by Skinner^ 
to be used directly by plants as a source of nitrogen, 
and to have produced a better growth of wheat seedlings 
than did an equivalent quantity of nitrogen in the form 
of sodium nitrate. Histidine, arginine, and creatine 
have also been found in soils and shown to be a direct 
source of nitrogen for wheat seedlings (par. 92). 

These and numerous other investigations of this subject 
show that amine as well as amide nitrogen is assimilated 
by at least some agricultural plants, but to what extent 
most of these compounds may successfully replace the 

1 Shorev, E. C. I. The Isolation of Creatinine from Soils. 
U. S. D. A., Bur. Soils, Bui. 8.3, pp. 11-22. 1911. 

^ Skinner, .1. J. III. Effects of Creatinine on Plant Growth. 
U. S. D. A., Bur. Soils, Bui. 83, pp. 33-44. 1911. 
2k 



498 SOILS: PROPERTIES AND MANAGEMENT 

inorganic forms of nitrogen has not been definitely worked 
out. Certain organic nitrogenous fertilizers — as, for ex- 
ample, dried blood — have a high commercial value, the 
nitrogen in this form selling for more a pound tiian the nitro- 
gen in any of the inorganic salts. jNIany crops, especially 
among garden vegetables, are most successfully grown only 
when supplied with organic nitrogenous material. Some 
nitrate nitrogen is always present luider natural soil con- 
ditions, so that crops are never limited to organic nitro- 
gen alone ; and it may be that the latter form of nitrogen 
is most useful when it supplements the nitrate nitrogen. 

420. Sodium nitrate. — This now constitutes the prin- 
cipal source of inorganic nitrogen in commercial fertilizers. 
The salt exists in the crude condition in northern Chili. 
The crude salt is purified by crystallization, and as put 
on the market it contains about 96 per cent sodium 
nitrate, or about 16 per cent of nitrogen, 2 per cent of 
water, and small amoiuits of chlorides, sulfates, and in- 
soluble matter. The cost of nitrogen in this form is 
from fifteen to eighteen cents a pound. 

Because of its easy availability, sodium nitrate acts 
quickly in inducing growth. For this reason it is used 
much by market gardeners, antl for other purposes when 
a rapid growth is desired. It is the most active form of 
nitrogen. A light dressing on meadowland in early 
spring assists greatly in hastening growth by furnishing 
available nitrogen before the conditions are faNorable 
for the process of nitrification. On small grain a similarly 
useful purpose is served where the soil is not rich. 

Owing to the fact that nitrate is not absorbed by the 
soil in large quantities, it is easily lost in the drainage 
water ; for this reason it should be applied onl>- when crops 
are growing on the soil, and then only in moderate quantity. 



COMMERCIAL FERTILIZERS 499 

The continued and abundant use of sodium nitrate 
on the soil may result, through its deflocculating action, 
in breaking down aggregates of soil particles, thus com- 
pacting and injuring the structure. This effect is attrib- 
uted to the accumulation of sodium salts, particularly 
the carbonate, as the sodium is not utilized by the plant 
to the same extent as is the nitrogen. 

421. Ammonium sulfate. — When coal is distilled, a 
portion of the nitrogen is liberated as ammonia and is 
collected by passing the products of distillation through 
water in which the ammonia is soluble, forming the am- 
moniacal liquor. The ammonia thus held is distilled into 
sulfuric acid, with the formation of ammonium sulfate 
and the removal of impure gases. 

Commercial ammonium sulfate contains about twenty 
per cent of nitrogen. It is the most concentrated form in 
which nitrogen can be purchased as a fertilizer, having 
from sixty to eighty pounds more of nitrogen to a ton 
than sodium nitrate. It is therefore economical to 
handle. Its effect on crops is not so rapid as that of sodium 
nitrate, but it is not so quickly carried from the soil by 
drainage water, as the ammonium salts are readily ab- 
sorbed by the soil. A pound of nitrogen in the form of 
ammonium sulfate has about the same agricultural value 
as the same amount in the form of nitrate if the soil on 
which it is used is abundantly supplied with lime ; but 
on an acid soil ammonium sulfate has less value. 

The long and extensive use of ammonium sulfate on a 
soil has a tendency to produce an acid condition, through 
the accumulation of sulfates which are not largely taken 
up by plants. 

Ammonium sulfate, like sodium nitrate, should not be 
applied in autumn, as the ammonia is converted into 



500 soils: properties and management 

nitrates and leached from the soil in sufficient quantities to 
entail a very decided loss of nitrogen. There is not likely 
to be so large a loss of nitrogen from ammonium salts as 
from nitrates, and, as would naturally be expected, there is 
greater loss of nitrogen when these salts are used alone than 
when they are combined with other fertilizing ingredients. 
Hall ^ has estimated the loss of nitrogen from certain 
drained plats at the Rothamsted Experiment Station. 
This estimate is based on the concentration of the drain- 
age from the different plats, of which there was no record 
of total flow, but for which the measurements of flow from 
the lysimeter draining GO inches of soil were taken and the 
total loss of nitrates was calculated on this basis. Esti- 
mated in this way the eft'ects of several different methods 
of manuring are shown in the accompanying table : — ■ 

Pounds to the Acre of Nitric Nitrogen in Drainage Water 





187£ 


)-80 


1880-81 


Treatment 


Spring 
sowing 

to 
harvest 


Harvest 

to 
spring 
sowing 


Spring 
sowing 

to 
harvest 


Harvest 

to 
spring 
sowing 


Unmanured 


1.7 


10.8 
13.3 

12.6 

15.6 

59.9 
14.3 

16.4 


0.6 
0.7 

4.3 

15.0 

3.4 
7.4 

3.7 


17.1 


Mineral fertilizers only 

Minerals + 400 pounds ammonium 
salts 


1.6 
18.3 


17.7 
21.4 


Minerals + 550 pounds nitrate of 


45.0 


41.0 


Minerals + 400 pounds ammonium 
salts applied in autumn .... 

400 pounds ammonium salts alone . 

400 pounds ammonium salts + sul- 
phatt» of potash 


9.6 
42.9 

19.0 


74.9 
35.2 

25.3 


Estimated drainage in inches . 


11.1 


4.7 


1.8 


18.8 



' Hall, A. D. The Book of the Rothamsted E.xperiraents, 
p. 235. New York, 1905. 



COMMERCIAL FERTILIZERS 501 

This table, in addition to confirming the statements 
already made in regard to the loss of nitrogen in drainage 
water, also shows how closely the supply of available 
nitrogen was used by the crops on those plats, which were 
evidently in need of nitrogen fertilization as the plats 
lost very little nitrogen during the growing season, while 
during the remainder of the year they lost nearly as 
much as did some of the nitrogen-manured plats. The 
table also indicates that the loss when nitrate is used is 
greater than when ammonium salts are applied, as the 
amount of nitrogen in the 550 pounds of nitrate is really 
eight pounds to the acre more than in the 400 pounds of 
ammonium sulfate, which is not sufficient to account for 
the difference in the loss. However, half of the nitrate- 
treated plat received no other manure and produced only 
a small crop, which would naturally result in a greater 
loss by drainage. 

422. Fertilizers containing atmospheric nitrogen. — 
The vast store of atmospheric nitrogen, chemically un- 
combined but very inert, will furnish an inexliaustible 
supply of this highly valuable fertilizing element, when it 
can with reasonable economy be combined in some manner 
resulting in a product that will be commercially trans- 
portable and that will, when placed in the soil, be or be- 
come soluble without liberating substances toxic to plants. 
The importance of the nitrogen supply for agriculture may 
be appreciated when it is considered that nitrates are 
being carried off in the drainage water of all cultivated 
soils at the rate of twenty-five to fifty pounds, and even 
more, to the acre annually, and that nearly as much 
more is removed in crops. 

The exhaustion of the supply of nitrogen in most soils 
may be accomplished within one or two generations of 



602 SOILS: propbhties and management 

men, unless a renewal of the supply is brought about in 
some way. Natural processes provide for an annual ac- 
cretion through the washing-down of ammonia and 
nitrates by rain water from the atmosphere, and through 
the fixation of free atmospheric nitrogen by bacteria ; but 
without the frequent use of legiuninous crops, the supply 
could not be maintained. Farm practice of the present 
day requires the application of nitrogen in some form of 
manure, and, as the end of the commercial supply of com- 
bined nitrogen is easily in sight, there is urgent need of 
discovering a new source. This has been done by com- 
bining calcium with atmospheric nitrogen in the forms of 
calcium cyanamide and calcium nitrate. 

423. Cyanamid. — The trade name for calcium cyana- 
mide is " cyanamid " and that name is therefore used 
in this volume. One process for the production of cyana- 
mid consists in passing nitrogen into closed retorts con- 
taining powdered calcium carbide heated to a high tem- 
perature ; the product being calcium cyanamide and free 
carbon : — 

CaCa + 2 X = CaCN2 + C 

The free carbon remains distributed in the cyanamide 
and gives the fertilizer a black color. The nitrogen re- 
quired for the process is obtained either by passing air 
over heated copper, or by the fractional distillation of 
liquid air. 

The fertilizer, as placed on the market, is a heavy, 
black powder or granulated material with a somewhat dis- 
agreeable odor. 

424. Composition of cyanamid.' — Cyanamid as maiui- 

' Cyanamid is a trade name ; the chemical compound is 
spelled cyanamide. 



COMMERCIAL FERTILIZERS 



503 



factured in this country has about the following composi 

tion : ^ — 

Calcium cyanamide 

Calcium carbonate 



Calcium sulfide 
Calcium phosphide 
Calcium hydroxide 
Free carbon . . 
Iron and alumina . 

Silica 

Magnesia . . . 
Combined moisture 
Free moisture . . 
Undertimed . . 



CaCNs 

CaCOa 

CaS 

CasPs 

Ca(0H)2 

C 

R2O3 

SiOo 

]MgO 

H2O 



Per cent 
45.92 
4.04 
1.73 
0.04 
26.60 
13.14 
1.98 
1.62 
0.15 
3.12 
0.35 
1.31 
100.00 
According to this composition the material would con- 
tain 16 per cent of nitrogen. Lime in the forms of carbo- 
nate and hydroxide would add somewhat to its value, 
and the residue of the calcium cyanamide, which upon 
decomposition is also calcium hydroxide, is likewise ben- 
eficial to the soil. 

425. Changes of calcium cyanamide in the soil. — 
Calcium cyanamide must be decomposed in the soil be- 
fore its nitrogen becomes available to plants. There 
are several steps in the decomposition process by which 
the nitrogen finally emerges in the form of ammonia. 
These, according to Pranke in the work just cited, con- 
sist first of hydrolysis, by which acid calcium cyanamide 
and calcium hydroxide are formed : — 

2 CX . NCa + H2O = (CX . XH)2Ca + Ca(0H)2 



calcium 
cyanamide 



acid calcium 
cyanamide 



calcium 
hydroxide 



1 Pranke, E. J. Cyanamid, p. 8. Easton, Pennsylvania. 1913. 



504 soils: properties and management 

The acid calcium cyanamide quickly loses its calcium, 
leaving free cyanamide. Investigators differ as to the 
process involved in this change, but the ultimate condi- 
tion of the calcium is carbonate. The three explanations 
of the process may be represented by the following re- 
actions : — 

1. (CX . NH)oCa + COo = 2 CX . XH2 + CaCOs 

In this reaction the carbon dioxide of the soil water is 
supposed to cause precipitation of the calcium. 

2. (CX . XH)2ra + 2 H2O = 2 CX . XH2 + Ca(0H)2 

In this case hydrolysis occasions the reaction. The 
hydroxide would, of course, be converted into carbonate 
in the soil. 

3. (CX . XH)2Ca + COo = CX . XH2 + CaCX2C02 

acid calcium carbon free calcium 

cyanamide dioxide cyanamide cyanamide 

carbonate 

CaCXaCOo + H2O = CX . XH2 + CaC03 

free calcium 

cyanamide carbonate 

By this reaction calciiun cyanamide carbonate is an in- 
termediate product, but is at once hydrolyzed and free 
cyanamide produced. 

The next step in the process is the formation of urea by 
hydrolysis of the free cyanamide : — 

CX . XH2 + II>0 = CO(XH2)2 

free cyanamide water urea 

The changes up to the production of urea are independent 
of bacterial action. The urea is converted through bac- 
terial action into ammonium carbonate : — 



COMMERCIAL FERTILIZERS 505 

CO(XH2)2 + 2 II2O = (NH4)2C03 

urea ammonium 

carbonate 

This may be converted into nitrates in the usual manner. 

426. The use of cyanamid. — The changes as here 
described are those that proceed under favorable condi- 
tions in the soil. When conditions are not favorable — 
as, for example, when a soil is saturated with water or 
when it is acid — some more or less injurious products 
may be formed. For this reason cyanamid is not likely 
to be so satisfactory on soils of this nature as on better 
soils. To very sandy soils it is not well suited. Ordi- 
narily its fertilizing value is not greatly below that of 
sodium nitrate, and is about equal to that of ammonium 
sulfate when not used in heavy applications. 

It should be incorporated with the soil at least a week 
before planting, as it may injure the young plants if de- 
composition has not proceeded far enough to remove its 
somewhat toxic properties. As it must undergo this 
decomposition before its nitrogen becomes available to 
the young plants, there is an added reason for this pre- 
caution. It does not give its best results as a top-dressing 
because it requires incorporation with the soil for its 
proper decomposition. 

427. Calcium nitrate. — The other process for com- 
bining atmospheric nitrogen is of more recent invention 
than that for the manufacture of calcium cyanamid but 
is not conducted on a commercial scale in this- country ; 
however, with the vast opportunities for developing elec- 
tric power which are offered in certain localities, factories 
for the manufacture of calcium nitrate will some day be 
established. 

The process employs an electric arc to produce nitric 



506 SOILS: PROPERTIES AND MANAGEMENT 

oxide by the combustion of atmospheric nitrogen, accord- 
ing to the simple equation : — 

NO + = NOo 

A very high power is required for this synthesis, in- 
volving a temperature of 2500'' to 3000° C, and the 
expense of the operation is determined almost entirely by 
the cost of the electricity. 

The nitric oxide gas is passed through milk of lime, 
giving basic calcium nitrate : — 

Ca(0H)2 + 2 HNO3 = Ca(N03)2 + 2 H2O 

The calcium nitrate resulting from this process has a 
yellowish white color, and is easily soluble in water but 
deliquesces very rapidly in the air. This last property 
can be overcome by adding an excess of lime in the manu- 
facture, thus producing a basic calcium nitrate which 
contains only 8.9 per cent of nitrogen. Another way of 
avoiding the difficulties involved by the deliquescent 
property of the nitrate is practiced by the factory at 
Nottoden, Norway. This consists in first melting the 
product, then grinding it fine and packing it in air-tight 
casks. The fertilizer thus prepared contains from 11 to 
13 per cent of nitrogen. 

Calcium nitrate contains its nitrogen in a form directly 
availal)lc to plants. It resembles sodium nitrate in its 
solubility, availability, and lack of absorption by the soil. 
It may be spread on the surface of the ground, as it exerts 
no poisonous action and does not tend to form a crust, as 
does sodium nitrate. 

The relative values of the different soluble nitrogen 
fertilizers vary with a great many conditions and can be 



COMMERCIAL FERTILIZERS 507 

accurately judged only by a large number of tests. At 
present, both calcium nitrate and cyanamid are being 
produced at less cost per pound of nitrogen than is sodium 
nitrate, when laid down in the neighborhood of the fac- 
tories in Europe. It seems fairly certain that, when the 
processes have been further improved, the result will be 
to greatly reduce the cost of available nitrogen. 

428. Organic nitrogen in fertilizers. — The commercial 
fertilizers containing organic nitrogen include cottonseed 
meal, which contains 7 per cent of nitrogen when free 
from hulls; linseed meal, with 5.5 per cent of nitrogen; 
castor pomace, with 6 per cent of nitrogen; and a num- 
ber of refuse products from packing houses, among which 
are red dried blood and black dried blood, the former 
having about 13 per cent of nitrogen and the latter from 
6 to 12 per cent; dried meat and hoof meal, with 12 to 
13 per cent of nitrogen ; ground fish, with 8 per cent of 
nitrogen ; and tankage, of which the concentrated product 
has a nitrogen content of from 10 to 12 per cent and the 
crushed tankage from 4 to 9 per cent ; also leather meal 
and wool-and-hair waste, but these, because of their 
mechanical condition, are of very little value. 

The meals made from seeds are primarily stock foods 
but are sometimes used as manures. They decompose 
rather slowly in the soil, owing to their high oil content, 
and are much more profitably fed to live stock than ap- 
plied as farm manure. They contain some phosphorus 
and potash as well as nitrogen. 

Guano consists of the excrement and carcasses of sea 
fowl. The composition of guano depends on the climate 
of the region in which it is found. Guano from an arid 
region contains nitrogen, phosphorus, and potassium, while 
that from a region where rains occur contains only phos- 



508 SOILS: PROPERTIES AND MANAGEMENT 

phorus — the nitrogen and potassium having been largely 
leached out. In a dry guano the nitrogen exists as uric 
acid, urates, and, in small quantities, ammonium salts. 
A damp guano contains more ammonia. The phosphorus 
is present as calcium phosphate, ammonium phosphate, 
and the phosphates of other alkalies. A portion of 
the phosphate is readily soluble in water. Thus all 
the plant-food either is directly' soluble or becomes so 
soon after admixture with the soil. The composition 
is extremely variable. The best Peruvian guano con- 
tains from 10 to 12 per cent of nitrogen, from 12 to 15 
per cent of phosphoric acid, and from 3 to 4 per cent of 
potash. 

Guano was formerly . a very important fertilizing ma- 
terial, but the supply has become so nearly exhausted 
that it is relatively unimportant at the present time. 

Of the abattoir products, dried blood is the most readily 
decomposed, and therefore has its nitrogen in the most 
available form. In fact, it produces results more quickly 
than any other form of organic nitrogen. It requires a 
condition of soil favorable to decomposition and nitrifica- 
tion, which prevents its exerting a strong action in early 
spring. It should be applied to the soil before the crop 
is planted. The black dried blood contains from 2 to 4 
per cent of phosphoric acid. 

Dried meat contains a high percentage of nitrogen, but 
does not decompose so easily as dried blood, and is not so 
desirable a form of nitrogen. It can be fefl to hogs or 
poultry to advantage, and the resulting manure is very 
high in nitrogen. 

Hoof meal, while high in nitrogen, decomposes slowly, 
being less active than dried blood. It is of use in increas- 
ing the store of nitrogen in a depleted soil. 



COMMERCIAL FERTILIZERS 609 

Ground fish is an excellent form of nitrogen, and is as 
readily available as blood but has a lower nitrogen content. 

Tankage is highly variable in composition, and the con- 
centrated tankage, being more finely ground, undergoes 
more readily the decomposition necessary for the utiliza- 
tion of the nitrogen. Crushed tankage contains from 3 to 
12 per cent of phosphoric acid, in addition to its nitrogen. 

Leather meal and wool-and-hair waste when untreated 
are in such a tough and undecomposable condition that 
they may remain in the soil for years without losing their 
structure. They are not to be recommeilded as manures. 

429. Availability of organic nitrogenous fertilizers. — 
The forms in which combined nitrogen is available to 
most agricultural plants has already been stated to be 
nitrates, ammonium salts, and certain organic compounds. 
Of the latter the simple compounds, as urea, appear to be 
most readily taken up by plants. Decomposition is there- 
fore a necessary process for most of these fertilizers, and 
their usefulness is, in general, proportional to the readi- 
ness with which aerobic decomposition proceeds, or to the 
proportion of available compounds that they contain in 
their original condition. Guano, for instance apparently, 
contains much nitrogen that is available without further 
decomposition. Dried blood quickly decomposes and 
soon forms available substances, consisting of the simpler 
organic nitrogenous compounds, ammonia and nitrates. 
The decomposition process is a biological one, arising from 
the action of microorganisms that first break down the 
complicated organic compounds, forming simpler ones, 
and finally carry the nitrogen into the form of ammonia, 
then to nitrous acid, and at last to nitric acid. 

Numerous attempts have been made to determine the 
relative availability of the nitrogen in various organic 



610 SOIL,S: PROPERTIES AND MANAGEMENT 

nitrogenous fertilizers. A few such tests, in which nitrate 
of soda and ammonium sulfate are used as a basis for com- 
parison, are given in the table below, the stJitement being 
in terms of percentage availability when nitrate of soda 
is taken as one hundred. The experiments quoted were 
conducted by Wagner and Dorsch,^ by Johnson, Jenkins, 
and Britton,- and by Voorhees and Lipman.^ 

Percentage Availability of Fertilizer Nitrogen 





Wagner 

AND 
DORSCH 


Johnson 

AND 

Others 


Voorhees 

AND 
LlPM.\N 


Nitrate of soda 

Sulfate of ammonia 

Dried blood 

Bone meal 

Stable manure 

Tankage 

Horn and hoof meal 

Linseed meal 

Cottonseed meal 

Castor pomace 

Wool waste 

Leather meal 

Dry ground fish 


100 
90 
70 
60 
45 

70 

30 
20 


100 

73 

17 

49 
68 
69 
65 
65 

64 


100 

70 
64 

53 



One difficulty in drawing conclusions from these experi- 
ments is that the sul)stances grouped under the same 
name are not always identical in the method of their 

1 Wagner, P., and Dorsch, F. Die Stiekstoffdiingung der 
Landw. Kulturpflanzen, Krstes Toil. Berlin. 1892. 

2 Johnson, S. W., .Jenldns, E. H., and Britton, W. E. Experi- 
ments on the Availability of Fertilizer-Nitrogen. Connecticut 
Agr. Exp. Sta., 21st Annual Rept., Part 4, pp. 257-277. 1807. 

' Voorhees, E. B., and Lipnian, J. G. Investigations Rela- 
tive to the Use of Nitrogenous Materials, 1898-1907. New 
Jersey Agr. Exp. Sta., Bui. 221. 1909. 



COMMERCIAL FERTILIZERS 511 

preparation or in their composition. Another discrep- 
ancy arises from the fact that all soils do not respond in 
the same relative degree to any one fertilizer. Thus, 
Sackett ^ found that in some soils dried blood was am- 
monified more rapidly than was cottonseed meal, while 
in other soils the reverse was true; and that a similar 
difference obtained in soils with respect to the ammoni- 
fication of alfalfa meal and flaxseed meal. It would 
therefore appear to be impossible to make any close dis- 
tinctions in the relative availability of the nitrogen in 
various organic nitrogenous fertilizers. A considerable 
number of these experiments are, in the aggregate, useful 
in pointing out the probable relative availabilities of the 
more widely differing nitrogen-bearing substances. 

FERTILIZERS USED FOR THEIR PHOSPHORUS 

Phosphorus is generally present in combination with 
lime, iron, or alumina. Some of the phosphates contain 
also organic matter, in which case they generally carry 
some nitrogen. Phosphates associated with organic 
matter decompose more quickly in the soil than do un- 
treated mineral phosphates. 

430. Bone phosphate. — Formerly bones were used 
entirely in the raw condition, ground or unground. When 
ground they act as a fertilizer more quickly than when 
unground. Raw bones contain about 22 per cent of phos- 
phoric; acid and 4 per cent of nitrogen. The phosphorus 
is in the form of tricalcic phosphate (Ca3(P04)2). 

Most of the bone now on the market is first boiled or 

' Sackett, W. G. The Ammonifying Eflfieieney of Certain 
Colorado Soils. Colorado Agr. Exp. Sta., Bui. 184, pp. 3-23. 
1912. 



512 SOILS: PROPERTIES AND MANAGEMENT 

steamed. This frees it from fat and nitrogenous matter, 
both of which are used in other ways. Steamed bone is 
more valuable as a fertilizer than raw bone, because the 
fat in the latter retards decomposition and also because 
steamed bone is in a better mechanical condition. The 
form of the phosphoric acid is the same as in raw bone 
and constitutes from 28 to 30 per cent of the product, 
while the nitrogen is reduced to l| per cent. 

Bone tankage, which has already been spoken of as a 
nitrogenous fertilizer, contains from 7 to 9 per cent of 
phosphoric acid, largely in the form of tricalcium phos- 
phate. All these bone phosphates are slow-acting ma- 
nures, and should be used in a finely ground form and for 
the permanent benefit of the soil rather than as an imme- 
diate source of nitrogen or phosphorus. 

431. Mineral ph sphates. — There are many natural 
deposits of mineral phosphates in different parts of the 
world, some of the most important of which are in North 
America. The phosphorus in all these is in the form of 
tricalcium phosphate, but the materials associated with 
it vary greatly. 

Apatite is found in large quantities in the provinces of 
Ontario and Quebec, Canada. It exists chiefly in crys- 
talline form. The tricalcium phosphate of which it is 
composed is in one form associated with calcium fluoride 
and in the other with calcium chloride. The Canadian 
apatite contains about 40 per cent of phosphoric acid, 
being richer than that found elsewhere. Phosphorite is 
another name for apatite, but is chiefly applied to the 
impure amorphous form. 

Coprolites are concretionary nodules found in the 
chalk or other deposits in the south of England and in 
France. Thev contain from 25 to 30 per cent of phos- 



COMMERCIAL FERTILIZERS 513 

phoric acid, the other constituents being calcium carbonate 
and siHca. 

South Carolina phosphate contains from 26 to 28 per 
cent of phosphoric acid and a very small amount of iron 
and alumina. As these substances interfere with the 
manufacture of superphosphate from rock, their presence 
is very undesirable — rock containing more than from 
3 to 6 per cent being unsuitable for that purpose. 

Florida phosphates exist in the form of soft phosphate, 
pebble phosphate, and bowlder phosphate. Soft phos- 
phate contains from 18 to 30 per cent of phosphoric acid, 
and because of its being more easily ground than most 
of these rocks it is often applied to the land without being 
first converted into a superphosphate. The other two 
forms, pebble phosphate and bowlder phosphate, are 
highly variable in composition, ranging from 20 to 40 per 
cent in phosphoric acid content. Tennessee phosphate 
contains from 30 to 35 per cent of phosphoric acid. 

Basic slag, or, as it is also called, phosphate slag or 
Thomas phosphate, is a by-product in the manufacture 
of steel from pig-iron rich in phosphorus. The phos- 
phorus present is usually considered to be in the form of 
tetracalcium phosphate, (CaO)4P205, or possibly a double 
silicate and phosphate of lime having the composition 
(CaO)5P205Si02. It contains also calcium, magnesium, 
aluminium, iron, manganese silica, and sulfur. Because 
of the presence of iron and aluminium, and because its 
phosphorus is more readily soluble than tricalcium phos- 
phate, the ground slag is applied directly to the soil with- 
out treatment with acid. 

The degree of fineness to which the slag is ground is 
supposed to be an important factor in determining its 
solubility in the soil. It is much more soluble in water 
2l 



514 SOILS: PROPERTIES AND MANAGEMENT 

charged with carbon (iioxi(h' tlian in pure water, a j)r()perty 
that greatly increases its vakie because of the fact that 
soil water always contains more or less of this gas. It is 
also readily acted upon by organic acids. For this reason 
it is particularly effective in a peat soil, and likewise in 
most soils deficient in lime. As it contains a considerable 
quantity of free lime it has another beneficial effect on 
such soils. 

432. Superphosphate fertilizers. — In order to render 
more readily available to plants the phosphorus contained 
in bone and mineral phosphates, the raw material, purified 
by being washed and finely ground, is treated with sulfuric 
acid. This results in a replacement of phosphoric acid by 
sulfuric acid, with the formation of monocalcium phos- 
phate and calcium sulfate, and a smaller amount of dical- 
cium phosphate, according to the reactions : — 

Ca3(P04)2+ 2 HoS04= CaH4(P04)o+ 2 CaS04 
Ca3(P04)2+ H.2S04= Ca2ri2(P04)2 + CaS04 

The tricalcium phosphate being in excess of the sul- 
furic acid used, some of it remains unchanged. 

In the treatment of phosphate rock some of the sul- 
furic acid is consumed in acting on the impurities present, 
which usually consist of calcium and magnesium carbo- 
nates, iron and aluminium phosphates, and calcium chlo- 
ride or fluoride, converting the bases into sulfates and 
freeing carbon dioxide, water, hydrochloric acid, and 
hydrofluoric acid. The resulting superphosphate is there- 
fore a mixture of monocalcium phosphate, dicalcium phos- 
phate, tricalcium phosphate, calcium sulfate, and iron and 
aluminium sulfates. 

In the superphosphates made from bone, the iron and 
aluminium sulfates do not exist in any considerable 



COMMERCIAL FERTILIZERS 515 

quantities. However, as long as the phosphorus remains 
in the form of monocalcium phosphate, the vahie of a 
pound of available phosphorus in the two kinds of fertilizer 
is the same ; but the remaining tricalcium phosphate has 
a greater value in the bone than in the rock superphosphate. 

The superphosphates made from animal bone contain 
about 12 per cent of available phosphoric acid and from 
3 to 4 per cent of insoluble phosphoric acid. They also 
contain some nitrogen. Bone ash and bone black super- 
phosphates contain practically all their phosphorus in an 
available form, but they contain little or no nitrogen. 
South Carolina rock superphosphate contains from 12 to 
14 per cent of available phosphoric acid, including from 
1 to 3 per cent of reverted phosphoric acid. The best 
Florida rock superphosphates contain from 17 per cent 
downward of available phosphoric acid, some of which is 
reverted. The Tennessee superphosphates contain from 
14 to 18 per cent of available phosphoric acid. 

Double superphosphates. — In making superphosphates 
a material rich in phosphorus must be used, not less than 
60 per cent of tricalcium phosphate being necessary for 
their profitable production. The poorer materials are 
sometimes used in making what is known as double super- 
phosphates. For this purpose they are treated with an 
excess of dilute sulfuric acid ; the dissolved phosphorus 
and the excess of sulfuric acid are separated from the mass 
by filtering, and are then used for treating phosphates 
rich in tricalcium phosphate and thus forming superphos- 
phates. The superphosphates so formed contain more 
than twice as much phosphorus as those made in the 
ordinary way. 

433. Reverted phosphoric acid. — A change sometimes 
occurs in superphosphates on standing by which some of 



516 SOILS: PROPERTIES AND MANAGEMENT 

the phosphoric acid becomes less easily soluble, and to 
that extent the value of the fertilizer is decreased. This 
change, known as reversion, is much more likely to occur 
in superphosphates made from rock than in those derived 
from bone. It will also vary in different samples, a well- 
made article usually undergoing little change even after 
long standing. It is supposed to be caused by the presence 
of undecom posed tricalcium phosphate and of iron and 
aluminium sulfates. 

434. Relative availability of phosphate fertilizers. — 
Superi)li()sphates and double superphosphates contain 
their phosphorus in a form in which it can be taken up 
by the plant at once. They are therefore best applied 
at the time when the crop is planted, or shortly before, 
or they may be applied when the crop is growing. Crude 
phosphates, on the other hand, become available only 
through the natural processes in the soil. They shouki 
be applied in quantity sufficient to meet the needs of the 
crops for a number of years. 

Reverted phosphorus, although not soluble in water, 
is readily soluble in dilute acids. It is now generally 
believed that in this form an available supply of phos- 
phorus is furnished to the plant. In a statement of fer- 
tilizer analyses reverted phosphorus is termed citrate- 
soluble, and this and the icater-soluble are termed available. 

The degree of fineness to which the material is ground 
makes a great difference in the availability of the less 
soluble phosphate fertilizers, especially in the ground-rock 
phosphates and in ground bone. This material should be 
ground fine enough to pass through a sieve having meshes 
at least one-fiftieth of an inch in diameter. 

435. Changes that occur when superphosphate is added 
to soils. — When incorporated with soils superphosphate 



COMMERCIAL FEIiTILIZEBS 517 

undergoes changes, the nature or which depends more or 
less on the properties of the particular soil with which it 
is mixed. No matter how readily soluble the phosphorus 
may be in the fertilizer, it soon becomes insoluble in the 
soil, only a fractional proportion of it being recoverable in 
water extracts. Absorption by colloidal complexes is the 
fate of a part of the phosphorus, in which condition it is 
still available to plants, especially when the colloidal 
matter becomes coagulated. The excess phosphorus en- 
ters into combination with the calcium of the soil, form- 
ing tricalcium phosphate and some dicalcium phosphate, 
and with the iron or the aluminium, forming phosphates of 
those metals. The latter compounds are less readily soluble 
than the former, and probably do not serve as a direct 
source of phosphorus for plants ; while tricalcium phosphate, 
although acted upon by plant roots, is not so readily a^'ail- 
able as is the phosphorus held by the colloidal matter. 

It is desirable that there should be an abundant supply 
of calcium in a soil to which a superphosphate is added, be- 
cause the phosphorus not absorbed by the colloidal matter 
of the soil will, under such circumstances, form more cal- 
cium phosphate than if only a small supply of lime is pres- 
ent, according to the law of mass action. The great loss 
of availability through the conversion of phosphorus into 
iron and aluminium phosphates may thus be mitigated. 

436. Other factors influencing the availability of tri- 
calcium phosphate. — As this is the form in which phos- 
phorus is probably most extensively held in the ordinary 
soil, and as it is also a cheap form of phosphorus in manures, 
it is a matter of some importance to know the most favor- 
able conditions for its utilization by agricultural plants. 
Experimentation by numerous investigators has estab- 
lished at least four factors that influence the availability 



518 SOILS: PROPERTIES AND MANAGEMENT 

of this substance : (1) kind of plant grown; (2) degree of 
basicity of soil ; Q]) fermentation of organic matter ; 
(4) character of the accompanying salts. 

437. Effect of plants on the availability of tricalcium 
phosphate. — It is to be expected that the various kinds 
of i)lants should not all exert an equal influence on the 
availability of the phosphorus of tricalcium phosphate. 
Prianischnikov ^ found that lupines, mustard, peas, 
buckwheat, and vetch responded to fertilization with raw 
rock phosphate in the order named, while the cereals did 
not respond at all. He did not include maize in his 
experiments, but that crop is said to respond well to diffi- 
cultly soluble phosphates. It is generally considered 
that those plants which have a long growing season are 
better able to utilize tricalcium phosphate than are more 
rapidly growing plants. An explanation for the ability 
of some plants to utilize the phosphorus of difficultly 
soluble phosphates more successfully than do other plants 
has been sought in the rate of excretion of carbon dioxide 
by plant roots. It has already been stated (par. 324) that 
Stoklasa and Ernst found that the capacity of a plant to 
absorb phosphorus from difficultly soluble phosphates is 
proportional to the rate at which carbon dioxide is given 
off by the roots, but that the experiments of Kossowitch 
and Barakoflf failed to confirm these results. This ques- 
tion is bound up with the larger one involving the solvent 
action of plant roots, regarding which little is now known. 

438. Effect of basicity on the availability of tricalcium 
phosphate. — It is recognized that raw rock phosphate is 
more available to the same plant in some soils than in 
others, and a number of persons have stated, as the result 

' Prianischnikov, D. Berieht iiber Verseliiedene Versuehe 
mit llohphosphaten unter Reduction. Moscow. 1910. 



COMMERCIAL FERTILIZERS 519 

of experimentation, that the availabihty is greater in acid 
soils than in those strongly basic. If acidity of the soil 
is due to the presence of free acid (positive acidity), it is 
conceivable that the availability may be due to the sol- 
vent action of the soil acid on the calcium of the trical- 
cium phosphate, producing the dicalcium salt which ap- 
pears to be fairly readily available to plants. When, 
however, soil acidity is due to a lack of basicity (apparent 
acidity), the case is different. Gedroiz ^ explains this 
on the basis of the absorptive properties of the apparently 
acid soil. He regards rock phosphate, not as a chemical 
compound, but as a solid solution of dicalcium phosphate 
with lime. It is this excessive basicity of the phosphate 
which is responsible for its unavailability. Absorption of 
the excess calcium would leave the phosphate in a more 
readily available condition by forming the dicalcium salt, 
and this is brought about in an apparently acid soil. 

Gedroiz experimented with a highly basic soil that did 
not respond to fertilization with rock phosphate. He 
subjected this soil to repeated washings with distilled 
water charged with carbon dioxide. After such treatment 
the soil gave a marked increase in crop with rock phos- 
phate as compared with the same soil untreated. Accord- 
ing to Gedroiz the greater availability of the phosphate 
after treatment with carbonic acid was due to the removal 
of bases and the greater absorptive power of the soil 
brought about thereby. This was further corroborated 
by the fact that the treated soil responded to a test for 
unsaturation while the untreated soil did not. Without 

^ Gedroiz, K. K. Soils to which Rock Phosphates may 
be Apphed with Advantage. Jour. Exp. Agronomy (Russian), 
Vol. 12, pp. 529-5.39, 811-816. 1911. The authors are in- 
debted to Dr. J. Davidson for the translation. 



520 SOILS: PROPERTIES AND MANAGEMENT 

necessarily accepting all of Gedroiz's explanation of the 
phenomenon, there can be little doubt that lack of basicity- 
is a factor in the availability of raw rock phosphates in 
some soils. 

439. Influence of fermenting organic matter. — There 
has been great difference of opinion among investigators 
as to the effect of fermentation of organic matter on the 
availability of the phosphorus of tricalcium phosphate. 
The contention that the availability is increased probably 
originated with Stoklasa/ the results of whose experi- 
ments with bone meal indicated that the availability is 
increased by fermentation. A large number of experi- 
ments have been conducted with raw rock phosphate 
composted with stable manure, among which may be 
mentioned those by Hartwell and Pember - and also by 
Tottingham and Hoffman ^ who in carefully conducted 
experiments failed to find that the availability of the raw 
phosphate was increased by fermentation with stable 
manure. Opposing results have also been obtained, how- 
ever, and the evidence is somewhat conflicting. Krober,^ 
who thinks that the action of bacteria is due to the acids 
they produce, explains the contradictions in the various 

1 Stoklasa, J., Duchacek, F., and Pitra, J. Ueber den Ein- 
fluss der Bakterien auf die Knoehenzersetzung. Centrlb. f. 
Bakt., II, Band 6, Seite 526-.'33.5, 554-558. 1900. 

'^ Hartwell, B. L., and Pember, F. R. The effect of cow dung 
on the availability of rock phosphate. Rhode Island Agr. 
Exp. Sta., Bui. 151. 1912. 

3 Tottingham, W. E., and Hoffman, C. The Nature of the 
Changes in Solubility and Availabihty of Phosphorus in Fer- 
menting Mixtures. Wisconsin Agr. Exp. Sta., Research Bui. 
29. 1913. 

* Krober, E. Ueber das Loslichwerden der Phosphor-siiure 
aus Wasserunlosliehen Verbindungen unter der Einwirkung 
von Bakterien und Hefen. Jour. f. Landw., Band 57, Seite 
5-80. 1909-1910. 



COMMERCIAL FERTILIZERS 521 

experiments as arising from the different kinds of fer- 
mentation that the organic matter undergoes. He thinks 
that acid fermentation renders the phosphate more readily 
sohible, while fermentation that does not give rise to acids 
leaves it in an insoluble condition. 

Parallel with the biological process that results in the 
transformation of insoluble phosphates into soluble, there 
is, according to Stoklasa and others, a reverse biological 
process resulting in the transformation of soluble phos- 
phates into insoluble. 

Whatever may be the conditions under which raw rock 
phosphate is rendered more readily soluble or available 
by fermentation of organic matter, it does not appear 
that composting with stable manure produces this change, 
at least from results of numerous experiments including 
those mentioned above. These have been mainly opposed 
to any such conclusion. 

440. Influence of other salts. — The presence of cer- 
tain salts has been found to influence the availability of 
difficultly soluble phosphates. The subject has been in- 
vestigated by a large number of experimenters and it will 
be possible to summarize their results only in part and 
very briefly. It has been found, for instance, that cal- 
cium .carbonate decreases the availability of raw rock 
phosphate and bone-meal. Sodium nitrate reduces the 
availability of the tricalcium phosphates, while the am- 
monium salts increase their availability. Iron salts 
decrease availability. The influence of other salts has not 
been so well worked out. Prianischnikov,^ as the result 
of his extended experiments on the subject, holds that 

1 Prianisehnikov, D. Ueber den Einfluss von Kohlensauren 
Kalk auf die Wirlcung von Versehiedenen Phosphaten. Landw. 
Vers. Stat., Band 7o, Seite 357-376. 1911. 



522 SOILS : PROPERTIES AND MANAGEMENT 

salts from which plants absorb acid in larger amounts 
than they do bases decrease availability, or at least do not 
affect it, while salts from which plants absorb the bases in 
greater quantity than the acids have a tendency to render 
the phosphate more available, because of the solvent 
action of the acid. 

FERTILIZERS USED FOR THEIR POTASSIUM 

The production of potassium fertilizers is largely con- 
fined to Germany, where there are extensive beds varying 
from 50 to 150 feet in thickness, lying under a region of 
country extending from the Harz Mountains to the Elbe 
River and known as the Stassfurt deposits. Deposits 
have lately been discovered in other parts of Germany. 

441. Stassfurt salts. — The Stassfurt salts contain 
their i)otassium either as a chloride or as a sulfate. The 
chloride has the advantage of being more diffusible in the 
soil, but in most respects the sulfate is preferable. Potas- 
sium chloride in large applications has an injurious effect 
on certain crops, among which are tobacco, sugar beets, 
and potatoes. On cereals, legumes, and grasses, the 
muriate appears to have no injurious effect. 

The mineral produced in largest quantities by the 
Stassfurt mines is kainit. Chemically it consists of mag- 
nesium and potassium sulfate and magnesium chloride, 
or of magnesium sulfate and potassium chloride. Kainit 
has the same effect on plants as has potassium chloride. 
It contains from 12 to 20 per cent of potash and from 25 
to 45 per cent of sodium chloride, with some chloride and 
sulfate of magnesium. 

Kainit should be applied to the soil a considerable 
time before the crop for which it is intended is planted. 



COMMERCIAL FERTILIZERS 523 

It should not be drilled in with the seed, as the action of 
the chlorides in direct contact with the seed may injure 
its viability. In addition to the potassium added to the 
soil by kainit, there are also in this fertilizer magnesium 
and sodium. The magnesium may be objectionable if 
there is much already present in the soil (see par. 458). 
Sodium may to some extent replace potassium in the soil 
economy, and in that way may be beneficial. 

Silvinit contains its potassium both as chloride and as 
sulfate. It also contains sodium and magnesium chlorides. 
Potash constitutes about 16 per cent of the material. 
Owing to the presence of chlorides, it has the same effect 
on plants as has kainit. 

The commercial form of potassium chloride generally 
contains about 80 per cent of potassium chloride or 50 
per cent of potash. The impurities are largely sodium 
chloride and insoluble mineral matter. The possible 
injury to certain crops from the use of the chloride has 
already been mentioned. For crops not so affected, potas- 
sium chloride is a quickly acting and effective carrier of 
potassium, and one of the cheapest forms. 

High-grade sulfate of potassium contains from 48 to 
50 per cent of potash. Unlike the muriate it is not in- 
jurious to crops, but is more expensive. 

There are a number of other Stassfurt salts, consisting 
of mixtures of potassium, sodium, and magnesium in the 
form of chlorides and sulfates. They are not so widely 
used for fertilizers as are those mentioned above. 

442. Wood ashes. — For some time after the use of 
fertilizers became an important farm practice, wood 
ashes constituted a large proportion of the source of supply 
of potassium. They also contain a considerable quantity 
of lime and a small amount of phosphorus. The product 



524 SOILS: PROPERTIES AND MANAGEMENT 

known as unleached wood ashes contains from 5 to 6 per 
cent of potash, 2 per cent of phosphoric acid, and 30 per 
cent of hme. Leached wood ashes contain about 1 per cent 
of potash, 1^ per cent of phosphoric acid, and from 28 to 29 
per cent of lime. They contain the potassimn in the form 
of a carbonate, which is alkahne in its reaction and in large 
amount may be injurious to seeds. They are beneficial 
to acid soils through the action of both the potassium and 
calcium salts. The lime is valuable for the other effects it 
has on the properties of the soil. (See pars. 454-457.) 

443. Insoluble potassium fertilizers. — Insoluble forms 
of potassium, existing in many rocks usually in the form 
of a silicate, are not regarded as having any manurial 
value. Experiments with finely ground feldspar have been 
conducted by a niunber of investigators, but have, in the 
main, given little encouragement for the successful use of 
this material. An insoluble form of potassium is not 
given any value in the rating of a fertilizer based on the 
results of its analysis. 

SULFUR AND SULFATES AS FERTILIZERS 

The use of these substances as a means of increasing 
plant growth when applied to soils has recently recei\'ed 
revived attention. The use of free sulfur has been in- 
vestigated to some extent in France and Germany. There 
have been suggested three ways in which it may be bene- 
ficial to plants (I) as a direct stimulant; (2) by its in- 
fluence on the activities of microorganisms; (8) as a 
source of plant-food, which might otherwise be deficient. 

444. The use of free sulfur. — • Boullanger ^ added 
flowers of sulfur to a soil at the rate of 23 parts to a million 

' Boullanger, E. Action du soufre en fleur sur la vegetation. 
Compt. Rend. Acad. Sci. Paris, T. 154, pp. 369-370. 1912. 



COMMERCIAL FERTILIZERS 625 

of soil. He obtained increased growth in all treated soils 
on which carrots, beans, celery, lettuce, sorrel, chicory, 
potatoes, onions, and spinach were grown, the weight of 
the crops on the treated soil being from 10 per cent to 40 
per cent greater than those on the untreated soil. On 
soils that had been sterilized before applying sulfur the 
effect was much less, from which he concludes that the 
beneficial effects were due to the influence of the sulfur 
on the microorganisms of the soil. There may be some 
question, however, whether this conclusion is justifiable. 
Sulfur was found by Boullanger and Dugardin ^ to favor 
ammonification in soils. Beneficial eflfects from the use 
of free sulfur have also been obtained by Demelon," and 
by Bernhard ^ among others, while von Feilitzen ^ found 
it to be ineffective as a fertilizer. 

That free sulfur may, under some conditions, exert a 
beneficial influence on plant growth must undoubtedly be 
conceded, but how the action is brought about remains to 
be conclusively demonstrated. Free sulfur is insoluble and 
cannot be absorbed by plant roots. However it is readily 
oxidized in soils ^ eventually producing sulfates with bases in 
the soil and in this form may readily be taken up by plants. 

1 Boullanger, E., and Dugardin, M. Meeanisme de Taction 
fertilisante du soufre. Compt. Rend. Acad. Sei. Paris, T. 155, 
pp. 327-329. 1912. 

^ Demelon, A. Sur Faction fertilisante du soufre. Compt. 
Rend. Acad. Sci. Paris, T. 154, pp. .524-526. 1912. 

5 Bernhard, A. Versuche iiber die Wirkung des Schwefels als 
Dung im Jahre 1911. Deutsche Landw. Presse. Band 39, p. 275. 
1912. 

* von Feilitzen, H. Ueber die Verwendung der Schwefel- 
blute zur Bekampfung des Kartoffelschorfes und als indirektes 
Dungemittel. Fuhling's Landw. Zeit. Band 62, Seite 7. 

* Mares, M. N. Des transformations que subit le soufre 
en poudre quand il es reponds sur le sol. Compt. Rend. Acad. 
Sci. Paris, T. 69, pp. 974-979. 



52G SOILS: PROPERTIES AND MANAGEMENT 

445. Sulfur as sulfate. — There is less experimental 
evidence rcfjarding the effect of sulfur in the form of 
sulfate on plant j^rowth than there is for the free sulfur. 
The fact that the bases with which the sulfate is com- 
bined are likely to have an effect on plant growth, makes 
the accumulation of j)r()of by experimentation a somewhat 
more difficult matter. That there may be a possible de- 
ficiency of sulfur in arable soils has been pointed out by 
several investigators, including Hart and Peterson ^ in 
this country. They point out that crops remo\e more 
sulfur from the soil than was shown by the early deter- 
minations of sulfur in plant ash, from which a large part 
of the sulfur was volatilized during the process. They 
then proceed to calculate the sulfur removed by a num- 
ber of crops on the basis of their own methods and 
compare this with the phosphorus in similar crops. 

Pounds Sulfur Trioxide and Phosphorus Pentoxide 
Removed to the Acre by Average Crops 



Crop and Yield to the Acre 



Content in Pounds to the 
Acre 



Wheat (30 bu.) 

Barley (40 bu.) 

Oats (45 bu.) 

Corn (30 bu.) 

Alfalfa (9000 lb. dry wt.) . . 
Turnips (4G57 lb. dry wt.) . . 
Cabbage (4800 lb. dry wt.) . . 
Potatoes (3360 lb. dry wt.) . . 
Meadow hay (2822 lb. dry wt.) 




» Hart, E. B., and Peterson, W. H. Sulphur requirements 
of farm crops in n-lation to the soil and air supply. Wise. 
Agr. p]xp. Sta., Research Bui. No. 14. 1911. 



COMMERCIAL FERTILIZERS 



527 



They then call attention to the quantities of sulfur 
trioxide contained in average soils which, as shown by 
Hilgard, are less than the quantities of phosphorus pen- 
toxide. 



Content in Pounds to the 

ACKE 




Sandy soils 
Clay soils . 



2610 
4230 



To ascertain whether the supply of sulfur in the soil 
is really depleted by cropping, the same authors made 
parallel determinations of sulfur in five virgin soils and 
in fi\e soils of the same respective types that had been 
cropped for sixty years. In each type the cropped soil 
contained less sulfur than the virgin soil, the average for 
the cropped soils being .053 per cent SO3 and for the 
virgin soils .085 per cent SO3. 

There is no doubt that the quantity of sulfur carried 
down by rain and snow is much less than that removed 
in drainage water. There can be no question therefore 
that most soils, and especially cultivated soils, are losing 
more sulfur than they receive by natural processes. 

It has been customary to add to soils manures of one 
kind or another that contain more or less sulfur. Among 
these are farm manure and other animal or bird excre- 
ments, residues of crops, animal offal, gypsum or land 
plaster, superphosphate, ammonium sulfate, potassium 
sulfate, kainit, and the like, all of which contain conse- 
quential quantities of sulfur. It seems probable that 



528 SOILS: PROPERTIES AND MANAGEMENT 

any system of soil management that does not include 
one or more of these substances would probably, on some 
soils at least, be improNed by making provision for the 
application of sulfur in some form. 

CATALYTIC FERTILIZERS 

The term catalytic fertilizers has been used rather 
loosely to designate a class of substances that, when added 
to a soil, increase plant growth by apparently accelerating 
the processes that normally take place in soils. They 
do not function as fertilizers because their \'alue does not 
lie in the nutrients that they possess, but they may 
properly be classed as soil amendments. However, 
substances not classed as catalyzers, such as lime, have 
such action, and in all probability most of the fertilizers 
do also, so that it is difficult to draw any definite distinc- 
tion and the term will doubtless be used only temporarily. 

446. Nature of catalytic action. — The term catalysis 
is employed in a chemical sense to mean a change brought 
about in a compound by an agent that itself remains 
stable. As an example of this may be cited the part that 
hydrochloric acid plays in the inversion of cane sugar, 
the acid not entering into the reaction but by its presence 
greatly accelerating it. When an attempt is made to 
stud}' these phenomena in soils, it becomes difficult, 
owing to the multiplicity of factors and reactions, to 
determine whether the agent is acting in a purely cata- 
lytic manner. 

447. Catalytic action of soils. — IMost soils themselves 
act as catalyzers in so far as they hasten the decomposition 
of hydrogen peroxide. Many substances, both organic 
and inorganic, have this property, and it is not necessarily 



COMMERCIAL FERTILIZERS 529 

entirely lost to the soil after the organic matter has been 
destroyed by ignition. It is therefore not due to an 
enzyme, as stated by Konig, Hasenbaumer, and Coppen- 
rath/ who first investigated the subject, nor entirely to 
organic substances in the soil. Doubtless there are several, 
or perhaps many, activating substances any of which have 
this property. It is altogether likely that other catalyzers 
exist in soils, and that they affect various reactions that are 
concerned in plant production. Among these substances, 
as pointed out by Konig, Hasenbaumer, and Coppenrath,^ 
are manganese and iron oxides, which are well known to 
exert catalytic action on certain reactions. While soils 
naturally possess certain catalytic powers, it seems possible 
to still further activate some soils by proper applications 
of so-called catalytic fertilizers. 

Organic matter is doubtless concerned in the catalytic 
properties of soils, and the investigators just mentioned 
found that in six soils the catalytic action stood in almost 
direct relation to the humus content ; Sullivan and Reid,^ 
however, did not find this correlation to hold. Both 
organic and inorganic substances are involved in this 
property of soils, but the forms in which they operate 
are not well understood. In the main productive soils 
have a strong catalytic effect and very poor soils are weak 
in this respect, but this correlation also is not constant. 



1 Konig, J., Hasenbaumer, J., and Coppenrath, E. Einige 
Neue Eigenschaften des Aokerbodens. Landw. Vers. Stat., 
Band 6.3, Seite 471-^78. 1905-1906. 

2 Konig, .J., Hasenbaumer, J., and Coppenrath, E. Bezieh- 
ungen zmschen den Eigenschaften des Bodens und der Nahr- 
stoffaufnahme durch die pflanzen. Landw. Vers. Stat., Band 
66, Seite 401-461. 1907. 

' Sullivan, M. X., and Reid, F. R. Studies in Soil Catalysis, 
U. S. D. A., Bur. Soils, Bui. 86. 1912. 
2m 



530 SOILS: PROPERTIES AND MANAGEMENT 

448. Substances used as catalytic fertilizers. — A 
lar<2;e number of substances liave been found to act as 
catalytic fertilizers. Among these are various salts of 
manganese, iron, aluminium, zinc, lead, copper, nickel, 
cobalt, uranium, boron, cerium, lanthanum, and the like. 
These substances stimulate plant growth when used in 
small quantities, and are toxic in large amounts. In 
water cultures a much less quantity of any of them is 
required to produce an injurious action on plant growth 
than when applied to an equal volume of soil. The 
absorptive properties of the soil and the less ready diffusi- 
bility serve to mitigate the toxic action. 

Different kinds of plants respond differently to the same 
concentration of any of these substances. For instance, 
Montemartini ^ found that uranium, copper, zinc, alumin- 
ium, and cadmium oxides retard the germination of beans 
and accelerate the germination of maize when used in equal 
concentrations. 

Of the various plant stimulants mentioned, manganese 
is the only one that gives promise, at the present time, 
of usefulness on a commercial basis, and it is the only one 
that will receive separate treatment in this book. 

449. Manganese. — It seems probable that all soils 
contain manganese, but the quantity present in some 
soils is very small, often being less than 0.01 per cent; 
in other soils, however, more than 1 per cent is found, 
and Kelly - reports an Hawaiian soil containing 9.74 per 



* Montemartini, L. Quoted with other experiments on this 
subject by N. H. J. Miller, in Annual Reports on the Progress 
of Chemistry, Vol. 10, i)]). 22!)-230. 1914. 

- Kelly, M. P. The Intlucnco of Manganese on the Growth 
of Pineapples. Jour. Indus, and Eng. Chem., Vol. 1, p. 533. 
1909. 



COMMERCIAL FERTILIZERS 531 

cent of Mn304. Sullivan and Robinson ^ examined 
twenty-six American soils and found the content of MnO 
to vary from 0.01 to 0.51 per cent, the average being 
0.071 per cent. 

INlanganese is a universal constituent not only of soils, 
but likewise of plants grown under natural conditions; 
in plants the quantities present vary much more than in 
soils, and range from a few tenths of one per cent to nearly 
one-half of the total ash. However, plants may be pro- 
duced in water cultures or other media in which apparently 
no manganese is present and a normal growth and fructi- 
fication will follow. It is evident, therefore, that any 
benefit to plant growth that may accrue through the 
addition of manganese to the soil is not due to its function 
as a nutrient material in the sense in which nitrogen, 
potassium, and phosphorus act in that capacity. 

450. Physiological role of manganese. — It was the 
discovery by Bertrand ^ of the existence of manganese in 
the oxidizing enzjTnes of plants and of its function in 
stimulating the oxygen-carrying power of these catalytic 
agents that suggested its use as a stimulating agent in 
crop production. In water cultures a very dilute solution 
of manganese salts increases plant growth, but beyond a 
very low concentration its effect is toxic. Plants differ 
widely in their response to manganese, with respect both 
to stimulation and to injury. A certain concentration 
may be stimulating to one plant and toxic to another. 

Experiments in the application of manganese salts 

1 Sullivan, M. X., and Robinson, W. O. Manganese as a 
Fertilizer, U. S. D. A., Bur. Soils, Circ. 75. 1912. 

^ Bertrand, G. Sur TAetion Oxydante des Sels Manganeux 
et sur la Constitution Chemique des Oxydases. Compt. Rend. 
Acad. Sei. Paris, Tome 124, pp. 1355-1358. 1897. 



532 SOILS: PROPERTIES AND MANAGEMENT 

to soils have not afforded as satisfactory results as have 
the trials with water cultures. Applications of a certain 
salt of manganese, when applied at the same rates to 
different soils, have in some cases produced increased 
growth, have in other cases had no apparent effect, and 
have in still other cases proved injurious to plants. The 
reason for this is doubtless to be found in the inherent 
properties of the particular soil to which the application 
is made. 

451. Action of manganese as a fertilizer. — The fact 
that manganese stimulates plant growth in water cultures 
is very good evidence that it has at least a direct action 
on the plant. Whether it has a further influence through 
reactions brought about in the soil is less e\'ident, although 
it seems likely that such is the case. Thus, Skinner and 
Sullivan ^ conclude from some of their experiments that 
oxidation in some soils is increased by the application of 
manganese salts. It also seems probable that manganese 
may have some influence on the activity of the microor- 
ganisms of the soil, but this has not been definitely demon- 
strated. 

452. Forms of manganese and response of soils. — 
The manganese salts that have been found to be effective 
as fertilizers are the sulfate, the chloride, the nitrate, the 
carbonate, and the dioxide. Of these the first has been 
most generally used, and in quantities up to 50 pounds 
an acre it has in most cases not been toxic. On acid 
soils it is not supposed to exercise any beneficial action, 
and on very productive soils Skinner and Sullivan, in 
the experiments cited above, found it to be ineffective; 



> Skinner, J. J., and Sullivan, M. X. The Action of Man- 
ganese in Soils. U. S. D. A., Bui, 42. 1914. 



COMMERCIAL FERTILIZERS 533 

while they obtained appreciable benefit from its use on 
poor soils. They argue that since very productive soils 
have great oxidative power the use of manganese is un- 
necessary, but since poor soils undergo insufficient oxida- 
tion the stimulation that this process receives by the 
application of manganese is productive of much good. 
Accordingly manganese is most profitably used on poor 
soils not deficient in lime. 



CHAPTER XXIV 
SOIL AMENDMENTS 

Certain substances are sometimes added to soils for 
the purpose of increasing productiveness through their 
influence on the physical structure of the soil, and thereby 
on the chemical and bacteriological properties. These 
substances are called soil amendments. It is true that 
they may add essential plant ingredients to the soil, but 
that function is of minor importance. 

453. Salts of calcium. — Calcium, although essential 
to plant growth, seldom needs to be added to the soil to 
supply the plant directly ; but because of its effect on the 
soil properties, its use is beneficial to a great number of 
soils. 

454. Effect on tilth and bacterial action. — On clay 
soils the effect of lime is to bring the fine particles into 
aggregates which arc loosely cemented by calcium carbon- 
ate. The effect of this structure on tilth has already been 
explained (par. 120). On sandy soils the carbonate of 
calcium serves to bind some of the particles together, 
making the structure somewhat firmer and increasing the 
water-holding power. It should be used only in small 
quantities on sandy soils. 

There is a tendency for most cultivated soils to become 
acid, as has already been explained (par. 283). Acidity 
may reach a point where it becomes directly injurious to 
certain plants, but it becomes indirectly injurious before 

534 



SOIL AMENDMENTS 535 

that point Is reached. One way in which this occurs is 
by curtailing the quantity of calcium carbonate in the 
soil. An easily available base to combine with the 
organic acids affords the most favorable condition for the 
decomposition processes due to bacterial action, and 
hence the best results cannot be obtained where carbonate 
of lime is not present. Its action in improving tilth also 
facilitates desirable forms of bacteriological activity by 
increasing the permeability of the soil for air. 

455. Liberation of plant-food materials. — It has been 
stated that the alkalies and the alkaline earths are more 
or less interchangeable in certain compounds in the soil. 
The addition of lime may in this way liberate potassium, 
when otherwise it would be difficult for crops to obtain 
a sufficient supply from a particular soil. The substitu- 
tion of bases has been discussed (par. 251) and the 
liberation of potassium is in accord with these phenomena. 
]\Iagnesium, although rarely deficient, may also be made 
available in this way. The use of calcium salts may, 
under some soil conditions, render phosphorus more use- 
ful, probably by supplying a base more soluble than iron 
or alumina, with which, in soils deficient in calcium, the 
phosphorus might otherwise be combined. Experiments 
by Prianischnikov,^ in which plants were grown in washed 
sand containing Hellriegel's nutrient solution to which 
mono-, di-, and tri-calcium phosphate respectively were 
added, both with and without calcium carbonate, showed 
a decreased availability of the tricalcium phosphate due 
to the presence of the carbonate, but neither a reduced 
nor an increased availability of the other forms of phos- 

' Prianischnikov, D. Ueber den Einfluss von Kohlensauren 
Kalk auf die Wirkung von Versehiedenen Phosphaten. Landw. 
Vers. Stat., Band 75, Seite 357-370. 1911. 



536 SOILS: PROPERTIES AND MANAGEMENT 

phorus arising from the presence of carbonate. Neither 
did the availabiHty of iron or aluminium phosphate 
appear to be influenced b\' calcium carbonate. 

These and recent experiments by Simmermacher ^ and 
others tend to discredit the earlier conclusions as quoted 
above and as set forth by Deherain - regarding the favor- 
able influence of lime on the availability of phosphorus. 
However, the preponderating e^•idence is still with the 
earlier experimenters. The principles that underlie the 
effect of lime on availability of phosphorus are discussed 
in paragraphs 259 and 260. 

456. Influence of lime on the formation of nitrates in 
soil. — It has already been remarked that nitrification 
proceeds very slowly in acid soils. A soluble base 
must be present with which the nitric acid may com- 
bine, otherwise the process will be inhibited by the toxic 
effect of the acid on the bacteria concerned in the forma- 
tion of the acid. The addition of lime is the most 
economical method of providing the base. This is 
often a matter of great moment for crops that respond 
readily to nitrate nitrogen, and is one of the important 
reasons for applying lime to sour soils. The fact that 
some plants grow better in some soils than in strongly 
basic ones is also an indication that such plants absorb 
a considerable part of their nitrogen in forms other than 
nitrates. 

Many investigators have found that the presence of 
calcium carbonate promotes the ammonifying and nitrify- 
ing process. The addition of calcium carbonate to a 

1 Simmermacher, W. Einwirkung der Kohlensauren Kalkes 
bei der Dungung von Ilaferkulturen mit IMono- und Dicalcium 
Phosphat. Landw. Vers. Stat., Band 77, Seite 441-471. 1912. 

' Deherain, P. P. Traite de Chemie Agricole, p. 525. 1892. 



SOIL AMENDMENTS 537 

sandy loam soil was found by Kellerman and Robinson ^ 
to favor the formation of nitrates up to an application 
of 2 per cent, which is much more than would ever be 
applied in practice. It must be kept in mind, however, 
that this limit does not apply to all soils, as the absorp- 
tive properties of the soil for lime will determine the 
maximum application that may profitably be made. 
Kellerman and Robinson found also that the application 
of magnesium carbonate in excess of 0.25 per cent in- 
hibited the formation of nitrates. Kelly ^ also has 
recently reported that the addition of magnesium car- 
bonate to the soils with which he experimented resulted 
in a marked depression of both ammonification and nitri- 
fication, and that the addition of calcium carbonate did 
not overcome this depressing influence. 

457. Effect on toxic substances and plant diseases. — 
Free acids are toxic to most agricultural plants. Some 
plants are much more sensitive than others. Alfalfa, 
for example, should have a slightly alkaline medium for 
its best growth, and any acid is very injurious. Calcium 
salts, in neutralizing acidity, remove this toxic condition. 
A liberal application of lime is therefore a precaution 
against injury of this kind. 

The presence of soluble calcium, with its effects on the 
soil, retards the development of certain plant diseases, 
such as the " finger and toe " disease of the Cruciferae. 
On the other hand, it may promote some diseases, as, for 
example, potato scab. 

1 Kellerman, K. F., and Robinson, P. R. Lime and Legume 
Inoculation. Science, n. s.. Vol. 32, pp. 1.59-160. 1910. 

2 Kelly, W. P. The Effect of Calcium and Magnesium Car- 
bonates on Some Biological Transformations of Nitrogen in 
Soils. Univ. of Calif. Pub., Agr. Sci., Vol. 1, No. 3, pp. 39-49. 
1912. 



638 SOILS: PROPERTIES AND MANAGEMENT 

458. The lime-magnesia ratio. — The physiological 
balancing of magnesium by calcium was first worked out 
by Loew/ and the ratio in which these two cations should 
exist in nutrient solutions in order to secure the best 
growth of certain agricultural plants has been very satis- 
factorily demonstrated by the experiments of many 
investigators. The optimum ratio varies with different 
kinds of plants, and in general the calcium must exceed 
the magnesium in amount, but there is a limit beyond 
which it should not be present. If calcium alone is 
present, it acts as a toxic agent on the plant, and mag- 
nesium acts in a similar way. It is only when the ratio 
between these cations falls within certain limits that 
they exert no toxic action. This ratio varies between 
one part of calcium oxide to one part of magnesium 
oxide, and seven parts of calcium oxide to one part of 
magnesium oxide. 

In the soil the relations of calcium and magnesium to 
plant growth are not so simple. It is impossible to 
determine the actual or the relative quantities of these 
cations that are available for absorption by the plant. 
This is mainly because of the absorptive properties of 
soils, by which they remove the bases from solution and 
hold them in a somewhat difficultly soluble form. The 
ratio of calcium to magnesium is not likely to disturb 
crop yields in soils unless the quantity of magnesium 
present happens to be very large. Gile and Ageton ^ 
have found ordinarilv fertile soils having ratios as high 



' Loew, O. The Physiological Role of the Mineral Nutrients 
of Plants. U. S. D. A., Bur. Plant Indus., Bui. 1, p. 53. 1901. 

2 Gile, P. P., and Ageton, C. U. The Significanoe of the 
Lime-Magnesia Ratio in Soil Analyses. Journ. Indus, and 
Eng. Chem., Vol. 5, pp. 33-35. 1913. 



SOIL AMENDMENTS 539 

as 500 CaO to 1 MgO by weight. On the other hand, 
excessive appHcations of magnesium compounds have 
been found to be injurious on some soils. Even on a 
very heavy clay soil, at Cornell University, an applica- 
tion of 1333 pounds to the acre of magnesite markedly 
decreased the yields of sorghum and oats. The soil 
originally contained about equal parts of calcium and 
magnesium. 

459. Forms of calcium. — Calcium is used on the 
soil in the form of calcium oxide, or quicklime (CaO), 
water-slaked lime (Ca(0H)2), air-slaked lime (CaCOs), 
ground limestone, marl (also a carbonate), and calcium 
sulfate, or gypsum (CaS04 . 2 H2O). The application of 
any of these is usually called liming the soil, although 
gypsum does not serve exactly the same purpose as do 
the other forms. Owing to differences in the molecular 
weights of these compounds of calcium, it requires more 
of some forms than of others to furnish the same amount 
of calcium. Approximately equivalent quantities of some 
of the common forms when fairly pure are : — 

Quicklime 56 pounds 

Water-slaked lime . 74 pounds 

Air-slaked lime, marl, and ground limestone 100 pounds 

Quicklime, and the hydrate, when added to the soil, even- 
tually assume some of the more insoluble forms of com- 
bination or remain as the carbonate, never being present 
as the oxide. It is always desirable to have present in the 
soil at least a small amount of calcium carbonate. 

460. Caustic limes. — Quicklime and water-slaked lime 
have a markedly alkaline reaction, and hence neutralize 
quickly any active acidity that may exist in the soil. 
They act quickly also in liberating plant-food, particularly 



640 SOILS: PROPERTIES AND MANAGEMENT 

nitrogen. Some soils respond more rapidly to quicklime 
or water-slaked lime than to carbonate of lime, e:>pecially 
when the carbonate is in the form of marl or ground lime- 
stone, these substances never being in such a finely pul- 
verized condition as is caustic lime. The use of the 
caustic forms of lime has been said to result in the loss 
of nitrogen by the too rapid decomposition of organic 
compounds. 

On clays the granulating effect of caustic lime is more 
marked than that of the carbonate, and for this reason 
the former has a distinct advantage for use on heavy clay. 
For the same reason an occasional moderate dressing is 
better than a heavy dressing given less frequently. 

461. Carbonate of lime. — Air-slaked lime has the 
advantage of being in a finely divided condition, and 
does not produce the injurious action on organic matter 
that is sometimes attributed to caustic lime. Its efi'ect 
on the granulation of clay soils is probably less pro- 
nounced than that of caustic lime. 

Marl (par. 27) differs from air-slaked lime principally 
in its property of being in a less finely pulverized condi- 
tion. It acts less quickly than does caustic lime. Owing 
to the fact that marl deposits differ greatly in the com- 
position of their products, it is well to know the quality 
of the material before buying it. The carbonate of lime 
in marl may vary from 5 or 10 to 90 or 95 per cent in 
different samples. 

Ground limestone has been used extensively in recent 
years. It is very important that it be finely ground, as 
on the comminution of the material much of its efficiency 
depends. However, it is doubtful whether there is any 
advantage in making it finer than is required to pass 
through a sieve with 50 meshes to the inch. 



SOIL AMENDMENTS 541 

462. Relative effectiveness of caustic lime and car- 
bonate. — In order to test the value of ground limestone 
and other forms of calcium carbonate, experiments in 
which it was compared with caustic lime have been con- 
ducted at some of the experiment stations. Reports of 
tests at the Pennsylvania Experiment Station/ in which 
plats treated with slaked lime at the rate of two tons per 
acre once in four years were compared with plats treated 
with ground limestone at the rate of two tons to the acre 
every two years, show that at the end of twenty years, 
in every case, the total yields were greater on the plats 
receiving ground limestone. After the treatment on 
these plats had been continued for sixteen years, a de- 
termination of nitrogen showed the upper nine inches of 
soil on the limestone-treated plats to contain 2979 pounds 
of nitrogen to the acre, and the slaked-lime plats to con- 
tain 2604 pounds. It may be inferred from these figures 
that the slaked lime caused a slightly greater destruction 
of organic matter than did the limestone. 

Patterson ^ also conducted experiments for eleven 
years with caustic lime produced by burning both stone 
and shells, and the carbonate of lime in ground shells and 
shell marl. The average crops of maize, wheat, and hay 
were all larger on the plats treated with carbonate of 
lime. 

\Vhile these experiments show, at first glance, results 

^ Waters, H. J., and Hess, E. H. General Fertilizer Experi- 
ments. Pennsylvania State College, Rept. 1894, Part 2, pp. 
258-281. Also, Hunt, T. F. Soil Fertility. Pennsylvania 
Agr. Exp. Sta., Bui. 90. 1909. 

^ Patterson, H. J. Lime, Sources and Relation to Agri- 
culture. Maryland Agr. Exp. Sta., Bui. 66, pp. 127-130. 1900. 
Also, Investigations on the Liming of Soils. Maryland Agr. Exp. 
Sta., Bui. 110, pp. 16-21. 1906. 



542 SOILS: PROPERTIES AND MANAGEMENT 

rather favorable to the use of carbonate of lime, a careful 
analysis of them by Wheeler ^ raises some doubt as to 
the legitimacy of this interpretation. He points out, for 
instance, that in the Pennsylvania experiments excessive 
quantities of lime were used, and that no farm manure 
nor commercial fertilizers were applied to the plats be- 
tween which comparisons were made. 

There is, unfortimately, a paucity of definite and con- 
clusive data that may be applied to the solution of the 
question as to the relative values of these different forms 
of lime for use as soil amendments, but some information 
has accumulated through experience and practice that 
may be taken as a fairly safe guide in their use. It is 
well known, for instance, that burned lime has a more 
pronounced effect on soil granulation than has the car- 
bonate, and may therefore be expected to be more bene- 
ficial to heavy clay soils. On the other hand, burned 
lime is not so desirable a form to apply to very sandy 
soils, especially when they are likely to be dry, as there 
is danger that organic matter will be destroyed. 

463. Sulfate of calcium. — Gypsum, in which form 
calcium sulfate is usually applied to soils, has been used 
for many years and was a popular soil amendment in 
this country before the common commercial fertilizers 
were used to any great extent. It frequently went by 
the name of l(ind plaster, and, as it was rather widely 
distributed in nature and not difficult to obtain, it was 
ground and largely used in many localities throughout 
the eastern states. Its popularity has waned in recent 

1 Wheeler, H. J. Is the Recoinniendation that Only Ground 
Limestone Should be Used for Agricultural Purposes a Sound 
and Rational One? National Lime Manufacturers' Assoc, 
Bui. 4. lUl'i. 



SOIL AMENDMENTS 543 

years, and its effectiveness has apparently decreased as 
the soils on which it was used have been longer under 
cultivation. Possibly this is due to the tendency of these 
soils to become more acid, which has caused the gypsum 
to be less effective in liberating potassium — a property 
with which it has generally been credited. At present 
gypsum is not very generally used on soils. It must be re- 
membered, however, that superphosphates always contain 
a considerable proportion of this material, and it may add 
appreciably to the beneficial effects of that fertilizer. 

Aside from its action in liberating potassium (the actual 
extent of which has never been very clearly demon- 
strated), gypsum serves to supply sulfur to the soil. The 
sulfur, while it may be needed in some soils, has the dis- 
advantage of being present as an acid ; and if the acid 
is added in larger quantity than is removed by plants, 
there is a resulting loss of basic material in the drainage 
water and a tendency for the soil to become sour. 

The action of gypsum in improving tilth is less marked 
than that of caustic lime or of the carbonate. As a source 
of calcium it is of no moment, as, if applied in such quan- 
tities as those in which the other forms are used, the 
sulfate would be very injurious. Ordinarily it is applied 
at the rate of only a few hundred pounds to the acre at the 
most. On the whole, gypsum is not an adequate substi- 
tute for, nor so desirable a form of, calcium as the oxide, 
the hydroxide, or the carbonate. 

464. Common salt. — Sodium chloride has a marked 
effect on some soils, but wherein its effectiveness lies 
is not well understood. The addition of sodium and of 
chlorine as plant constituents is clearly not the reason, 
as these substances are always present in soils in avail- 
able form far in excess of their requirements. 



544 SOILS: PROPERTIES AND MANAGEMENT 

The effect of sodium chloride on clay-bearing soils 
is to liberate certain plant nutrients, among which are 
calcium, magnesium, potassium, and phosphorus. This 
action, although limited in amount, is probably, in some 
cases at least, partly responsible for the beneficial action 
of common salt. 

The structure of the soil is improved by the applica- 
tion of sodium chloride, just as it is by lime, although 
usually not to the same extent. 

Another effect of salt is to conserve and distribute 
soil moisture. Its conserving action is probably due to 
an increase in the density of the soil-water solution, thus 
retarding transpiration. The film movement of water is 
likewise increased by the presence of salt in the solution, 
and in this way the upward movement of bottom water 
is facilitated and the supply within reach of the roots 
maintained in time of drought. 

It has been seen that sodium is not one of the substances 
essential to the growth of plants. But that sodium may 
be substituted, in part, for the potassium absorbed by 
agricultural plants in their normal growth, has been 
shown in this country by the experiments of Wheeler 
and Adams ; ^ and the more ready availability of the 
sodium applied as a chloride than of the potassium in 
its natural condition in some soils probably accounts in 
part for the beneficial effects of this salt. 

It is not all soils, however, that are benefited by salt, 
its usefulness not being of such wide application as that 
of lime. Certain crops, as previously mentioned, are 
injured by the presence of chlorine. 

* Wheeler, H. J., and Adams, G. E. Concerning the Agri- 
cultural Value of Sodium Salts. Rhode Island Agr. Exp. Sta., 
Bui. 106. 1905. 



SOIL AMENDMENTS 545 

465. Muck. — The effect of muck (par. 72) is to 
change the structure of soils, making a heavy clay soil 
lighter and more porous, and binding together the par- 
ticles of a sandy soil. Both classes of soils, but particu- 
larly the sandy type, have a greater water-holding 
capacity after treatment with muck, owing to its great 
absorpti\'e power which amounts to 70 per cent or more 
of its own weight. It is to its content of organic matter 
that the physical effects of muck are due. 

Muck contains 1 to 2 per cent of organic nitrogen, 
calculated to dry matter, which does not readily undergo 
ammonification. The addition of farm manure (which 
ferments readily) and of lime serves to hasten ammoni- 
fication. Its use as an absorbent in the stable fits it well 
for use on the land. 

Very large applications of muck are necessary when 
it is used to improve the structure of the soil. From 
ten to forty or fifty tons per acre are frequently applied. 

Muck has been used successfully as a carrier of Bacillus 
radicicola; for this it is eminently adapted by its absorbent 
qualities, which prevent it from drying out and thus caus- 
ing injury to the bacteria. At the rate of thirty pounds 
to the acre it has served as a highly effective medium for 
inoculating soil for alfalfa.^ 

Muck is also used as a filler in certain commercial 
fertilizers. 

1 Lyon, T. L., and Bizzell, J. A. Some Experiments in Top- 
Dressing Timothj' and Alfalfa. Cornell Univ. Agr. Exp. Sta., 
Bui. 339. 1913. 



2n 



CHAPTER XXV 
FERTILIZER PRACTICE 

The purchase and use of commercial fertilizers in an 
economical way requires not only specific technical 
knowledge of the various materials, as already set forth, 
but also a certain amount of general knowledge both 
practical and theoretical. There are at present so many 
fertilizing materials on the market under various trade 
names, that the question as to the best one to buy for a 
certain crop growing under definite soil and climatic 
conditions becomes a difficult one. The greater the 
general knowledge, therefore, that a person possesses 
as to the effects of the different elements on plant growth, 
as to fertilizer inspection and control, as to methods of 
buying, as to home mixing, as to methods and time of 
application, and as to mixtures for special crops, the 
better he is able to utilize fertilizers that will result in 
financial gain. That a fertilizer shall be profitable is 
the ultimate desideratum. ^loreover, as all fertilizers 
exert, either directly on indirectly, a residual effect, the 
problem necessarily broadens into a study of the systems 
of applying fertilizers to a series of crops or to a rotation, 
rather than a study of the effects of one particular ferti- 
lizer application on one particular crop. 

Note. — For discussions of fcrtiliz(>r practice see TTalligan, J. E., 
Soil Fertility and Fertilizers, Chapters 13-17. Easton, Penn- 
sylvania. 1912. Also, Van Slyke, L. L. Fertilizers and Crops, 
Chapters 21-25, and 27-35. New York, 1912. Also, Fraps, 
G. S. Principles of Agricultural Chemistry, Chapter IG. Eas- 
ton, Pennsylvania. 1913. 

546 



FERTILIZER PRACTICE 547 

466. Effects of nitrogen on plant growth.^ — Of the 
three primary elements of a fertilizer, nitrogen - seems 
to have the quickest and most pronounced effect, not 
only when present in excess of the other constituents, 
but also when moderately used. It tends primarily to 
encourage aboveground vegetative growth and to impart 
to the leaves a deep green color, a lack of which is usually 
due to insufficient nitrogen. It tends in cereals to in- 
crease the plumpness of the grain, and with all plants it 
is a regulator in that it governs to a certain extent the 
utilization of potash and phosphoric acid. Its application 
tends to produce succulence, a quality particularly de- 
sirable in certain crops. In its general effects it is very 
similar to moisture, especially when supplied in excessive 
quantities. 

The peculiarity of nitrogen lies not only in its absolute 
necessity for plant growth, its stimulation of the vegeta- 
tive parts, and its close relationship to the general tone 
and vigor of the crop, but also in the fact that it was not 
one of the original elements of the earth's crust. During 
the formation of the soil it slowly and gradually became 
present, brought down by rains and fixed naturally in the 
soil itself mostly through the agency of bacterial action. 
Even now it exists largely locked up in complex nitrog- 
enous compounds of the humus and the less decayed 
organic matter, and becomes slowly available to plants 

1 Discussions of the effects of the various elements on plants 
may be found as follows: Russell, E. J. Soil Conditions and 
Plant Growth, Chapter IT, pp. 19-50. London, 1912. Also, 
Hall, A. D. Fertilizers and Alanures, Chapters III, V, and VI. 
New York, 1910. 

- For a discussion of nitrogen in relation to crop yield, see 
Hunt, T. F. The Importance of Nitrogen in the Growth of 
Plants. Cornell Univ. Agr. PLxp. Sta., Bui. 247. 1907. 



548 SOILS: PROPERTIES AND MANAGEMENT 

largely through bacterial activity. It may be stated with 
certainty that one of the possible limiting factors to 
crop growth is a lack of water-soluble nitrogen at critical 
periods in amounts necessary for normal crop develop- 
ment. Since soluble nitrogen may be very readily lost 
from the soil by leaching, the problem of proper plant 
nutrition becomes a serious one. Not only must the 
farmer be able to so regulate its addition in fertilizers 
as to obtain the highest efficiency, but he must understand 
the control and encouragement of the natural fixation 
as well. The emphasis placed on all phases of the nitrogen 
problem serves to reveal its great importance in fertility 
practices. 

Because of the immediately visible effect from the ap- 
plication of soluble nitrogen, the average farmer is prone 
to ascribe too much importance to its influence in proper 
crop development. This attitude is unfortunate, since 
nitrogen is the highest-priced constituent of ordinary 
fertilizers. Moreover, of the three primary elements 
it is the only one which added in excess will result in 
harmful after effects on the crop. Its general influences, 
besides its functions in the metabolic and synthetic 
processes of plant development, may be listed briefly as 
follows : 

1. Nitrogen teiuls to increase the growth of the above- 

ground parts. 

2. It delays maturity by encouraging vegetative growth. 

This oftentimes endangers the crop to frost, or 
may cause trees to winter badly. 

3. It increases the ratio of straw to grain in cereals, and 

the ratio of leaves to underground parts in root 
crops. 



FERTILIZER PRACTICE 549 

4. It loeakens the straw and causes lodging in grain. This 

is due to an extreme lengthening of the internodes, 
and as the head fills the stem is no longer able to 
support the increased weight. 

5. It lowers quality. This is especially noticeable in 

certain grains and fruits, as barley and peaches. 
The shipping qualities of fruit and vegetables are 
also impaired. 

6. It increases the percentage of nitrogen in the crop, 

particularly in the straw of cereals and in timothy 
hay. 

7. It decreases resistance to disease. This is probably due 

to a change in the physiological resistance to disease 
within the plant, and also to a thinning of the cell 
wall, allowing a more ready infection from without. 

While certain plants, as the grasses, lettuce, radishes, 
and the like, depend for their usefulness on plenty of 
nitrogen, for the average crop it is generally better to 
limit the amount of nitrogen so that growth may be 
normal. This results in a better utilization of the nitro- 
gen and in a marked reduction of the fertilizer cost for a 
unit of crop growth. This is a vital factor in all fertil- 
izer practice, and shows immediately whether fertilization 
is or is not an economic success. 

467. Effects of phosphorus on plant growth. — It is 
difficult to determine exactly the functions of phosphoric 
acid in the economy of even the simplest plants. Neither 
cell division nor the formation of fat and albumen go on 
to a sufficient extent without it. Starch may be pro- 
duced when it is lacking, but will not change to sugar. 
As grain does not form without its presence, it very 
probably is concerned in the production of nucleoproteid 



550 SOILS: PROPERTTES AND MANAGEMENT 

materials. Its close relationship to cell division ma.\ 
account for its ))resence in seeds. Its general effects ( 
plant growth may l)e listed as follows : 



)n 



1. Phosphorus hastens maturity by its effect on rate of 

ripening. This makes phosphorus especially valu- 
able in wet years, and in cold climates where the 
season is short. 

2. It increases root development, especially of lateral and 

fibrous rootlets. This renders it valuable with 
such soils as do not encourage root extension and 
to such crops as naturally have a restricted root 
development. Phosphorus is therefore valuable in 
fall-sown crops, in years of drought, and for farm- 
ing on arid land. 

3. It decreases the ratio of straw to grain by hastening the 

filling of the grain and by promoting maturity. 

4. It strengthens the straw, due to its balancing effect on 

the nitrogen. 

5. It improves the quality of the crop. This has been 

recognized in the handling of pastures in Englantl 
and France. The effect on vegetables is also 
marked. 

6. It increases percentage of phosphorus in the crop. 

With cereals this is particularly noticeable in the 
st^aw^ 

7. It increases resistance to disease, due probably to 

more normal cell development. 

Excessive phosphorus ordinarily has no bad effect, 
as it does not stimulate any part excessively as does ni- 
trogen, nor does it lead to a development which is detri- 
mental. Its lack is not quickly apparent, as in the case 



FERTILIZER PRACTICE 551 

of nitrogen, and as a consequence phosphorus starvation 
may occur without any suspicion thereof being enter- 
tained by the farmer. 

One of the most important phases to be noted from this 
comparison of the effects of nitrogen and phosphorus is 
the balancing powers of the latter on the unfavorable in- 
fluences generated by the presence of an undue quantity 
of the former. This is a vital factor in fertilizer practice, 
since normal fertilizer stimulation always results in the 
most economic gains. Such a normal increase is obtained 
only when the plant functions of the several fertilizer 
constituents are in proper accord. 

468. Effects of potassium on plant growth. — The 
effects of potash are more localized than those of nitrogen 
and phosphorus. Potash is essential to starch formation, 
either in photosynthesis or in translocation, and is a 
necessary component of chlorophyll. It is important 
in grain formation, giving plump, heavy kernels. In 
general it tends to impart tone and vigor to a plant. In 
increasing resistance to disease it tends to counteract 
the ill eifects of too much nitrogen, while in delaying 
maturity it works against the ripening influences of 
phosphoric acid. In a general way it exerts a balancing 
effect on both nitrogen and phosphate fertilizer materials, 
and consequently is necessary in a mixed fertilizer, es- 
pecially if the potash of the soil is lacking or unavail- 
able. As with phosphorus, it may be present in large 
quantities in the soil and yet exert no harmful effect on 
the crop. 

469. Law of the minimum. — In connection with the 
obvious importance of utilizing, for any particular soil 
and crop, a fertilizer well balanced as to the three primary 
elements, two queries naturally arise. These are : 



552 SOILS: PROPERTIES AND MANAGEMENT 

(1) What are the right proportions of nitrogen, phos- 
phorus, and potash to apply under given conditions? 

(2) What would be the effect if any one of these should 
not be present in such a quantity as to make it equal in 
function to the others? The first query cannot be dis- 
posed of until the question of fertilizer mixtures has been 
considered. The second, however, is not affected by so 
many factors, and is more clearly a question of the func- 
tion of the elements concerned. 

Any element that exists in relatively small amounts as 
compared with the other important constituents natu- 
rally becomes the controlling factor in croj:) de\elopment. 
Any reduction or increase in this element will cause a 
corresponding reduction or increase in the crop yield. 
This element, then, is said to be " in the minimum." 
In fertilizer practice, ideal conditions would exist if no 
constituent functioned as a decided minimum and the 
entire influence of each single element were fully utilized. 
In other words, the fertilizer would be balanced as to its 
relationship to normal plant growth. That such a con- 
dition is more or less ideal and theoretical is obvious, 
from the fact that the various fertilizer carriers undergo 
more or less radical changes after being applied to the 
soil. The composition of the soil itself is also a disturb- 
ing factor. Nevertheless, the nearer an approach can be 
made to such conditions, the greater will be the economy 
of fertilizer practice. 

Numerous persons have investigated the question as 
to what effect an increase of an element in the minimum 
may have on crop yield, and various ideas have been 
advanced thereon. The idea of a definite law governing 
the increase of plant growth according as the element 
in the minimum is increased, was first suggested by 



FERTILIZER PRACTICE 553 

Liebig. Wagner ^ later stated definitely that up to a 
certain point the increase yield was proportional to the 
increase in the application. This, however, evidently 
cannot apply except over a very limited field, since it is 
a matter of common observation that increased crop 
yield becomes lower as the lacking element is supplied. 
Recently INIitscherlich ^ has formulated a law ^ which is a 
logarithmic, rather than a direct, function of the increase 
in the element occupying the position of the minimum. 
jMitscherlich's law may be stated concisely as follows : 
the increased growth produced by a unit increase of the 
element in the minimum is proportional to the decre- 
ment from the maximum. The following curve (see 
Fig. 62) constructed from data obtained by IN'Iitscherlich,^ 
shows the trend of the increased growth curve as governed 
by increased applications of an element in the minimum, 
other factors being, of course, under control. This curve 
is maintained by Mitscherlich to approximate a theoretical 
curve of a definite mathematical formula. 

1 Wagner, 11. Beitrage ziir Dungerlehre. Landw. Jahr., 
Band 12, Seite 691 £f. 1883. 

^ Mitscherlich, A. E. Das Gesetz des Minimums und das 
Gesetz des Abnehmen den Bodenertrages. Landw. Jahr., 
Band 38, Seite 537-552. 1909. 

Also, Ein Beitrage ziir Erforsehung der Ausnutzung des 
im Minimum Vorhandenen Nahrstofifes durch die Pflanze. 
Landw. Jahr., Band 39, Seite 13.3-156. 1910. 

— ^ = (a — y)k. Integrating, log {a — y)= c —kx. 
dx 

y = total yield from any number of increments. 

X = amount of any particular fertilizer constituent utilized. 

a = ma.ximum yield and is a constant. 

A: = a constant depending on y and x, variables. 
* Mitscherlich, A. E. tjber das Gesetz des Minimums und 
die sich aus diesem Ergebenden Schlussfolgerungen. Landw. 
Ver. Stat., Band 75, Seite 231-263. 1911. 



554 SOILS: PROPERTIES AND MANAGEMENT 



60 










. i 


SO 


/" 


^ 




















3/9/ 












/o 












10 





























/ 







2.0 



SRAMsS P^Os PEf3 POT 

Fig. 62. — Curve showing the increased growth of oats under the in- 
fluence of constantly increasing amounts of phosphorus, that ele- 
ment being in the minimum. 

The formula as proposed by jMitscherlich has been 
questioned by several investigators/ who have shown 
that a number of conditions, such as light, heat, and 

1 Pfeiffer, Th., Blanck, E., and Flugcl, AI. Wasserund Licht 
als Vegetationsfakloroii und ihre Bezieliungfon zum (Jesetze vom 
Minimum. Landw. Ver. Stat., Band 76, Seite 211-22.3. 1912. 

Also, Maze, P. Recherehes sur les Relations de la Plante 



FERTILIZER PRACTICE 555 

moisture, tend to disturb the application of such a law. 
The fact that crop yield is the summation of so many 
varying factors seems to argue in favor of no hard and 
fast rule regarding the increased growth due to the added 
increments of an element in the minimum. It is enough, 
in the practical utilization of fertilizers, to remember that 
this curve in general approximates the one already cited, 
and that in order to obtain the best results from a com- 
plete fertilizer a mixture should be used that is approxi- 
mately balanced so far as the effects of the elements are 
concerned, the crop as well as the chemical constitution 
of the soil being considered. 

470. Fertilizer brands. — In an attempt to meet the 
demands for well-balanced fertilizers suited to various 
crops and soils, manufacturers have placed on the market 
numberless brands of materials containing usually at 
least two of the important elements, and nearly always 
the three ; the former being designated as incomplete 
fertilizers, while the latter are spoken of as complete 
fertilizers. These various brands usually have some 
catchy name, such as " The Ureka Corn Special," " Far- 
mers' Potato and Corn Fertilizer," " The Golden Har- 
vest," or " The Empire State Sure Crop Phosphate." 
Such a name frequently implies the usefulness of the 
material for some particular crop, but oftener it has no 
relation either to crop or to soil. Ordinarily the name 
should be ignored in the purchase of fertilizers. 

A brand of fertilizer is usually made up of a number 
of materials containing the important ingredients. These 
materials, already described, are called carriers. The 
making-up of a commercial fertilizer consists, then, in 

avec les Elements Nutritifs du Sol. Compt. Rend., Vol. 154, 
pp. 1711-1714. 1912. 



556 SOILS: PROPERTIES AND MANAGEMENT 

merely mixing the various carriers together so that the 
required percentages of nitrogen, potash, and phosphoric 
acid are obtained, care being taken that no detrimental 
reaction shall occur and that a physical condition con- 
sistent with easy distribution shall be maintained. If 
the substances used are difficultly soluble, the fertilizer 
is not so valuable as one composed of easily soluble con- 
stituents. The general solubility of the various in- 
gredients should be known by a prospective purchaser. 

The various brands on the market, besides being 
complete or incomplete, may be designated as high-grade 
or low-grade. These terms may be used in two ways — 
high-grade or low-grade as to availability, or high-grade 
or low-grade as to amount of plant-food constituents 
carried. A low-grade fertilizer in the percentages of 
nitrogen, phosphoric acid, and potash is always encum- 
bered with a large amount of inert material, which adds 
to the cost of mixing, transportation, and handling. It 
is thus usually a more expensive fertilizer to a unit of 
plant-food obtained than one of higher grade. Except 
for special purposes, a low-grade fertilizer as to avail- 
ability should be bought sparingly or not at all. 

471. Fertilizer inspection and control. — With the 
many different materials available for mixing commercial 
fertilizers, and from the fact that so many opportunities 
are open for fraud either as to availability or as to guaran- 
tee, laws have been found necessary for controlHng the 
sale of fertilizers. Most states have such a law, the 
western laws generally being superior to those in force 
in eastern states, where the fertilizer sale is heavier. 
This is because the western regulations are more recent 
and the legislators have had the advantage of the ex- 
perience gained where fertilizers have long been used. 



FERTILIZER PRACTICE 657 

Moreover, the legislators in such states have not been so 
strongly confronted with fertilizer lobbying, and have 
consequently been free to enact stricter laws than were 
possible where fertilizers are such an important com- 
mercial commodity. 

Usually certain provisions are common to all fertilizer 
laws. In general, all fertilizers selling for a certain price 
or over (usually $5 a ton) must pay a state license fee and 
print the following data on the bag or an authorized tag : — 

1. Number of net pounds of fertilizer to a package. 

2. Name, brand, or trade-mark. 

3. Name and address of manufacturer. 

4. Chemical composition or guarantee. 

The composition of a commercial fertilizer is ordinarily 
expressed simply; for example, as a 3-6-10, meaning 3 
per cent of nitrogen, 6 per cent of phosphoric acid, and 
10 per cent of potash. This, however, is too brief for a 
guaranteed analysis on goods exposed for sale, as it gives 
no idea whatsoever regarding the solubility of the ma- 
terials. As might be expected, there is a wide range in 
the character of the guarantee required by the various 
states. For example, some states insist on the statement 
of the percentage of both nitrogen and ammonia, while 
others insist only on the percentage of nitrogen. Some 
require the soluble, the reverted, and the total phosphoric 
acid, while others require only the soluble and the re- 
verted. As to potash, in some cases the soluble must be 
stated, while in other cases the total must be given. In 
general, a guarantee should show not only the amount 
of the various constituents, but also their form or avail- 
ability. The guarantee required by North Dakota is 
excellent in this respect : — 



558 SOILS: PROPERTIES AND MANAGEMENT 

Guarantee required by the State of North Dakota 

Percentage of N in nitrates Percentage of P2O5 soluble 
Percentage of N as ammonia in water 

Percentage of N total Percentage of P2O5 re- 

verted 
Percentage of P2O5 in- 
Percentage of K2O soluble soluble 

Percentage of K2O as chloride Percentage of P2O5 total 

Since a fertilizer law is designed primarily to protect 
not only the purchasers but also the manufacturers, a 
certain amount of variation is allowed below a guarantee. 
This is a matter of extreme variation in the different states. 
Ordinarily, also, the offering for sale of any leather matter 
or its products, either separately or in mixtures, is pro- 
hibited, unless so stated specifically on the package. 

For the enforcement of such laws, the states usually 
provide adequate machinery. The inspection and analyses 
may be in the hands of the state department of agricul- 
ture, of the director of the state agricultural experiment 
station, of a state chemist, or under the control of an\' 
two of these. In any case, a corps of inspectors is pro- 
vided, the members of wliich take samples of the fertilizers 
on the market throughout the state. These samples are 
analyzed in laboratories provided for the purpose, in 
order to ascertain whether the mixture is up to its guar- 
antee. If the fertilizer falls below the guarantee, — allow- 
ing, of course, for the variation permitted by law, — the 
manufacturer is subject to prosecution. 

A more eifective check on fraudulent guarantees, how- 
ever, is found in publicity. The state law usually pro- 
vides for the pul)lication each year of the guaranteed and 
found analyses of all brands inspected. Not only has 



FERTILIZER PRACTICE 559 

this proved eflFectivo in preventin*!; fraud, but it is really 
a great ad\'antage to the honest manufacturer. 

The expenses for the inspection and control of fertilizers 
are usually defrayed by the license fees, which average 
for the different states from ten to twenty dollars a year 
for each brand selling for $5 or more a ton. In the 
eastern states this fee produces a net return greatly in 
excess of the expenses incurred by the fertilizer inspection 
and control, and consequently has become the source of 
a handsome income for these states. 

472. Trade values of fertilizers. — It has become cus- 
tomary for the authorities charged with fertilizer inspec- 
tion and control in the various states to adopt each year 
a schedule of the trade values of the various elements as 
they appear on the market in unmixed lots. These 
values are obtained by averaging all the wholesale prices 
of a ton for the various unmLxed supplies for the six 
months preceding j\Iarch 1, to which is added 20 per cent 
of the price to cover cost of handling. The trade values 
for 1912 were as follows: ^ — 

Trade Values of Plant-pood Elements in Raw Ma- 
terials AND Chemicals 

Cents a pound 

Nitrogen in ammonia salts 18| 

Nitrogen in nitrates 18^ 

Organic nitrogen in dry and fine fish, meat, and blood 20 

Organic nitrogen in fine bone, tankage, and mixed 

fertilizer 19 

Organic nitrogen in coarse bone and tankage . . 15 
Organic nitrogen in castor pomace and cottonseed 

meal 20 

1 New York (Geneva), Agr. Exp. Sta., Bui. 371, p. 434. 1913. 



560 SOILS: PROPERTIES AND MANAGEMENT 

Cents a pound 

Phosphoric acid, water-soluble 4^ 

Phosphoric acid, citrate-soluble (reverted) ... 4 

Phosphoric acid, in fine bone, fish, and tankage . 4 
Phosphoric acid, in cottonseed meal and castor 

pomace 4 

Phosphoric acid, in coarse fish, bone, tankage, and 

ashes 3| 

Phosphoric acid in mixed fertilizers, insoluble in 

water or ammonium citrate 2 

Potash as high-grade sulfate, in forms free from chlo- 
rides, in ashes, etc. 5j 

Potash as muriate 4| 

Potash as castor pomace and cottonseed meal . . 5 

It must be remembered that these prices are seaboard 
evaluations, and represent the cost to the manufacturer 
of the elements as they exist in the unmixed carriers. 
This is called the commercial evaluation of a fertilizer, 
and is the first of a number of items that enter into the 
total cost, or the price the farmer must pay on the retail 
market. The items that make up this ultunate price 
may be listed as follows : (1) retail cash cost, or com- 
mercial evaluation ; (2) cost of mixing ; (3) profit of 
manufacturers ; (4) transportation ; (5) storage, com- 
mission to agents, bad debts, and so forth ; and (6) profit 
of retailer. These additional charges are often sufficient 
to double the original commercial value of the fertilize 
constituents. 

It is evident that by knowing the composition of a fer- 
tilizer, and the carriers of the various constituents, the 
commercial evaluation of the mixture may be easily cal- 
culated. However, what the farmer must pay depends 



FERTILIZER PRACTICE 561 

to a large extent on the additional charges already listed. 
Thus, a fertilizer evaluated at $22 a ton on the New York 
market may cost the farmer $35, or even $45, after having 
passed through the hands of the manufacturer and the 
retail merchant. This commercial evaluation, however, 
must not be confused with the agricultural evaluation, 
which is the value of the increased crop produced by the 
application of the fertilizer. It is evident that the agri- 
cultural value will vary with the soil, the crop, or the 
season, and may be above or below the total cost accord- 
ing to circumstances. In good fertilizer practice, the 
excess of the agricultural value over the total cost of the 
fertilizer, all costs incidental with the growing, harvest- 
ing, and marketing of the increase being first deducted, 
should be sufficient to give a handsome profit on the 
investment. 

473. The buying of mixed goods. — The successful 
buying of mixed fertilizers on the retail market depends 
on two things : (1) the selection of a suitable composi- 
tion, with carriers of known value ; and (2) the purchase 
of high-grade goods. The farmer who observes these 
two points will have at least purchased successfully. 
Whether he obtains a profit from the use of the fertilizer 
depends on the balancing of a number of factors more or 
less variable from season to season. 

The selection of a suitable fertilizer, as to carriers and 
composition for any particular crop or soil, entails first 
of all a study of the guarantee. Should the guarantee 
be such as that already cited, a large amount of informa- 
tion is at hand concerning the forms of the carriers and 
the availability of the important constituents. This 
knowledge, properly correlated with the probable needs 
of the crop and the soil, will determine whether that 
2o 



562 SOILS: PROPERTIES AND MANAGEMENT 

particular brand should be purchased or not. The real 
question here is not the actual quantities of the elements 
in a ton of the fertilizer, but their balance among them- 
selves. The actual pounds of nitrogen, phosphoric acid, 
or potash applied per acre can be governed by the rate 
at which the mixture is applied. 

The purchase of high-grade goods is the second impor- 
tant point to be considered. Data collected from practi- 
cally every state show that the higher the grade of the 
fertilizer, both as to availability and as to the percentage 
of the constituents carried, the greater is the amount of 
})lant-food obtained for every dollar expended. The 
following data, taken from Vermont ^ for 1909, are the 
average of one hundred and thirty brands and are typical 
data in this regard : — 



Fertilizer 


S -J 
o > 


aH 
" as 

f^ J a 

Is! 

a « o 

02 O H 


, o 


<-" a a 

C3 J « 
2 «" 

S a 6. 

Dfe O 

o ta 5 


Cost (in Cents) 
OF One Pound op 


OS >> 

a » 
2 a o 
J > a 
rH a 
« « 2; 
n a; bj 

fe h. ^ 

fcj aW 

°^« 
a « <: 




N PjOs 


KsO 


P a rJ 
J O J 

^ a o 


Low grade 


$13.52 


$27.10 


$13.58 


$1.00 .38 


7.6 


(cents) 

8.5 50.0 


Medium 
















grade . 


18.22 


30.00 


11.78 


0.65 


.31 


6.3 


7.0 60.6 


High grade 


26.30 


38.93 


12.63 


0.48 


.28 


5.7 


6.3 67.6 



It is noticeable at once that the lower the grade of the 
fertilizer, the higher is the proportional cost of placing 
the goods on the market. In other words, it costs just 



' Hills, J. L., Jones, C. H., and Miner, H. L. Commercial 
Fertilizers. Vermont Agr. Col., Bui. 143, pp. 147-149. 1909. 



FERTILIZER PRACTICE 563 

as much per ton to market a low-grade material as a 
high-grade one. This accounts for the fact that the ele- 
ments are cheaper per pound in a high-grade mixture, 
and that the value of plant-food received for e^'ery dollar 
expended is greater. 

474. Home-mixing fertilizers. — In comparing the above 
commercial evaluations with the prices actually paid 
by the farmer on the retail market, it is found that the 
latter shows an increase ranging from 48 to 100 per cent. 
This is due to the charges for mixing, transportation, han- 
dling, storage, commission, interest on capital, profit, 
and other items, made during the passage of the material 
from the wholesale dealer to the user. In order to escape 
these costs, many farmers have begun the practice of 
buying the separate carriers, thus avoiding these charges 
— except, of course, that of transportation. In many 
cases the mixing on the farm costs nothing, as it can be 
done in winter when the farm work is not pressing. Even 
if the farmer must charge himself with this mixing, it 
seldom amounts to more than fifty cents a ton. 

As might be expected, this practice has met with much 
opposition from manufacturers. In general it is claimed 
that the factory goods are more finely ground than those 
mixed by the farmer, and consequently the ready-mixed 
goods are not only more uniform but also in better physi- 
cal condition. Also, the manufacturer is able to treat 
certain materials with acids, and thus increase their 
availability. While these reasons are more or less valid, 
good results may be expected from a fertilizer even though 
it may not be quite uniform, as the soil tends to equalize 
this deficiency. Moreover, by screening and by using 
a proper filler, a farmer can obtain a physical condition 
which will in no way interfere with the drilling of the ma- 



5G4 SOILS: PROPERTIES AND MANAGEMENT 

terial. While, obviously, one farmer alone cannot afford 
to buy direct from the wholesale dealer because of the 
high freight charges on small lots, this objection is being 
met by clubs and various organizations whereby the 
single carriers may be bought in carload lots. 

It is evident that when a farmer mixes his own fertilizer 
he is able to obtain not only pure goods, but high-grade 
goods as well, thus reducing freight. jMoreover, as a gen- 
eral thing home mixing is cheaper than buying the ready- 
mixed goods. A quotation from Connecticut ^ for 190G 
illustrates about what this saving may be : — 

Plant-Food Purchased for $30 



Nitrogenous superphosphates 

Best quality .... 

Least valuable . . . 
Special manures 

Best quality .... 

Lowest quality 
Home mixtures 

Average of all . . . . 



Pounds 

N 



73 
23 

69 
32 

77 



Pounds 
P2O6 



188 

279 

170 
174 

200 



Pounds 
K2O 



111 

53 



Total 



372 
355 



143 ' 382 
66 272 

168 



445 



A third point, and by some considered to be more im- 
portant than those already discussed, is the educational 
value of home mixing. No farmer can mix his own fertil- 
izer without becoming familiar with the carriers, their 
availability, and their effects. He is forced to study their 
influence on the crops more closely, and thus is placed 



'Jenkins, E. H., and Winton, A. L. Fertilizer Report. 
Conn. (New Haven) Agr. Expt. Sta., Kept. 1906, Part I, pp. 
1-100. 



FERTILIZER PRACTICE 565 

in a position to make changes that will tend to a higher 
efficiency of the constituents. The chances are that he 
will alter his fertilizer mixture as his rotation progresses 
and his soil changes in fertility. 

Such arguments do not always mean, however, that 
it pays to mix at home. As a matter of fact, in many 
cases it does not pay, especially where only a small amount 
of fertilizer is needed and it is impossible to cooperate 
with other farmers. As a general rule, fertilizers should 
be bought by the method that will give the greatest value 
for every dollar expended. Farmers often can avail 
themselves of the advantage of both systems by asking 
for bids from various manufacturers on carload lots of 
mixed goods having a certain designated composition. 
The farmers in this case designate the carriers as well. 
All the advantages of machinery mixing may thus be 
gained, with the lower cost which has made home mixing 
so popular. 

475. Fertilizers not to be mixed. — Every farmer who 
practices home mixing should keep in mind that there 
are certain fertilizers which should not be mixed. This 
is due to the fact that a number of materials carry lime 
in the oxide, the hydrate, or the carbonate form. This 
lime, particularly the caustic forms, may react in three 
directions, depending on the fertilizer with which it is in 
contact: (1) in setting free ammonia, (2) in causing re- 
version of acid phosphate, and (3) in producing a bad 
physical condition, especially when in contact with ma- 
terials more or less deliquescent. Van Slyke ^ may be 
quoted in this regard as follows : — 



1 Van Slyke, L. L. Fertilizers and Crops, pp. 485-486. 
New York, 1912. 



566 SOILS: PROPERTIES AND MANAGEMENT 



1. 



2. 



Calcium oxide 
Calcium hydrate 
Wood ashes 
Basic slag 
Calcium cyanamid 
Basic calcium 
nitrate 

Calcium oxide 
Calcium hydrate 
Calcium carbonate 
Wood ashes 
Basic calcium 
nitrates 

Calcium oxide 
Calcium hydrate 
Basic calcium 
nitrate 



should not be 
mixed with 



ammonium sul- 
fate 

animal manures, 
as tankage, 
blood, and the 
like 

nitrogenous 
guanos 



1 11 X i_ f soluble phos- 
should not be i , 

, .^, \ phates 
mixed with „ , . , 

or any kind 



should not be 
mixed with 
(unless applied 
immediately) 



sodium nitrate 
potassium chlo- 
ride 
kainit, and the 
like 



Neither is it wise to allow moist acid phosphate to lie 
in contact with large quantities of sodium nitrate, as 
nitric acid may be slowly liberated by free sulfuric or 
phosphoric acid. Also, large quantities of calcium cyana- 
mid should not be mixed with acid phosphate because 
of the lime contained in the former. If, however, the 
ratio is not greater than one to ten, the results are bene- 
ficial, since the reaction, without causing serious rever- 
sion of the phosphate, generates enough heat to quickly 
season the mixture. The fine and dry condition of the 
cyanamid is also conducive to a good mechanical condi- 
tion, and accounts for tlie fact that this material is in 
such favor with manufacturers of mixed gootls. 



FERTILIZER PRACTICE 567 

476. How to mix fertilizers. — As the various carriers 
are bought uiider guarantee, the percentages of nitrogen, 
phosphoric acid, and potash in the ingredients to be mixed 
are accurately known. The calculation of the amounts 
of each carrier and of the filler necessary to make up a 
ton of a fertilizer having a certain formula, then becomes 
a matter of simple arithmetic. The mixing is an equally 
simple operation. The implements needed in home mixing 
are as follows: (1) a tight floor, (2) platform scales, 

(3) a sand screen with from three to six meshes to an inch, 

(4) a tamper or a grinder, (5) shovels, a rake, and like 
tools. 

First, the various ingredients, after being crushed and 
screened if lumpy, are weighed out in amounts sufficient 
for the unit of fertilizer to be mixed at any one time. 
The bulkiest material is spread on the floor first and leveled 
uniformly by raking. The remaining ingredients are 
then spread in thin layers above the first, in the order 
of their bulk. Beginning at one side, the material is 
next shoveled over, care being taken that the shovel 
reaches the bottom of the pile each time. The pile is 
then again leveled, and the process is repeated a sufficient 
number of times to insure thorough mixing. Sometimes 
a mixing machine may be used for this operation. For 
storage and general convenience, the fertilizer may be 
weighed into sacks of from 100 to 150 pounds capacity 
and put in a dry place until needed for use. 

A word of caution should be inserted here regarding the 
concentration of the mixture. Some farmers, in order 
to lessen the work of mixing and application in the field, 
raise the percentage of the elements exceedingly high — 
a condition very likely to occur when high-grade materials 
are used. This is bad practice, in that it may interfere 



568 SOILS: PROPERTIES AND MANAGEMENT 

with germination and may also injure the young plants. 
Also, it is likely to result not only in a poor physical condi- 
tion but also in uneven distribution, which will bring about 
a lowered efficiency of the fertilizer. The use of sufficient 
dry, finely divided filler will obviate such dangers. 

477. Factors affecting the efficiency of fertilizers. — 
The agricultural value of a fertilizer is necessarily a vari- 
able quantity, since, in applying fertilizers, a material 
subject to change is placed in contact with two wide 
variables, the soil and the crop. The general factors 
that govern the effect of fertilizers may be listed as 
follows : — 

1. Seed, crop, and adaytaiion of crop to soil. — It is quite 

evident that difi'erent crops will respond differ- 
ently to the same fertilizer elements. Also, the 
strength of the seed, the management of the crop, 
and the adaptation of crop to soil, will be potent 
factors in variation. 

2. Temperature, sunshine, and rainfall. — These factors 

are meteorological and, of course, are dominant 
in the growth of the plant. Rainfall especially 
is important, as an optimum moisture content 
is conducive to good plant development. In 
general, as shown by experiments in Ohio and 
Pennsylvania, the higher the rainfall, the greater 
is the efficiency of the fertilizer used. 

3. Drainage. — This is of great importance in ferti- 

lizer practice, since it places the soil in a better 
condition from all standpoints for plant growth. 
In other words, the better the normal soil condi- 
tions, the better should be the reaction from ferti- 
lizer application. 



FERTILIZER PRACTICE 669 

4. Physical condition of the soil. — The addition of lime 

and organic matter, the utilization of drainage, 
tillage, and the like, all are conducive to higher 
crop returns through the indirect effect on fertilizer 
efficiency. 

5. Lime. — Lime, by improving physical conditions, 

by setting plant-food free, by correcting acidity, 
by stimulating bacterial action, and by tending 
to eliminate toxic materials either directly or 
indirectly, is of great importance in fertilizer 
practice. In fact, certain fertilizers, such as 
ammonium sulfate and acid phosphate, do not 
reach their full efficiency unless plenty of lime is 
present. 

6. Organic matter. — Besides the effect of organic matter 

on physical conditions and chemical reactions 
which indirectly influence fertilizer action, an im- 
portant action is set up by organic matter in the 
encouragement of bacterial functions. As the 
favorable changes of fertilizers, especially those 
carrying nitrogen, is due to biological activity, 
the presence of organic materials becomes doubly 
important. 

7. Chemical coviyosition of the soil. — Since the full 

return from a fertilizer is derived when the ele- 
ments are well balanced, the actual constitution 
of the soil becomes a factor, especially when ready 
availability is obtainable. Therefore, in choosing 
a fertilizer and deciding on the amounts to apply, 
the chemical condition of the soil is no mean factor. 

While the conditions affecting fertilizer efficiency have 
thus been so briefly disposed of, it is evident that a more 



670 SOILS: PROPERTIES AND MANAGEMENT 

detailed consideration of the question would be not only 
interesting but also profitable, would space permit. One 
point of broader scope, however, than the addition of a 
well-balanced food stimulation, stands out clearly in this 
consideration. The necessity of putting a soil in any 
given climate into the best possible condition for plant 
growth is paramount. This means that drainage, lime, 
humus, and tillage, in the order named, must be raised 
to their highest perfection. Under such improvements 
the further use of commercial fertilizers may or may not 
be a paying investment. 

478. Method and time of applying fertilizers. — The 
distribution of the fertilizer by means of machinery is 
much more satisfactory than is broadcasting by hand, 
as the former method gives a more uniform distribution. 
Cereals and other crops are now usually planted with a 
drill or a planter provided with an attachment for dropping 
the fertilizer at the same time that the seed is sown, the 
fertilizer being by this method placed under the surface 
of the soil. Broadcasting machines are also used, which 
leave the fertilizer uniformly distributed on the surface 
of the ground, thus permitting it to be harrowed in suffi- 
ciently before the seed is planted, and preventing injury 
to the seed by the chemical activity of the fertilizing 
material. 

Corn planters with fertilizer attachments deposit 
the fertilizer beneath the seed, thus avoiding a possible 
detrimental contact. Grain drills do not do this, and, 
where the amount of fertilizer used exceeds 300 or 400 
pounds an acre, it is better to apply it before seeding. 
Grass and other small seeds should be planted only after 
the fertilizer has been mixed with the soil for several 
days. For crops to which large quantities of fertilizers 



FERTILIZER PRACTICE 571 

are to be added, especially potatoes and garden crops, 
it is desirable to drop only a portion of the fertilizer with 
the seed, the remainder having been broadcasted by ma- 
chinery and harrowed in earlier. 

479. Fertilizing crops. — Three primary considerations 
must be observed in the actual utilization of fertilizers : 
(1) the percentage of nitrogen, phosphorus, and potash 
suited to the crop and the soil ; (2) the availability of the 
carriers ; and (3) the amounts to be applied. It is evi- 
dent, due to so many factors that are difficult to control, 
that fertilizer formulas for different crops on particular 
soils are difficult to determine. In fact, such data can 
never be more than merely suggestive. Further, the 
best quantity of a mixture to apply, even though it is 
perfectly balanced, is a figure that can only be approxi- 
mated. Probably the largest percentage of the fertilizer 
waste that occurs annually can be charged to this factor. 
Many farmers make the mistake of applying too much 
fertilizer. As a consequence, any information along such 
lines can only be merely suggestive, rather than literal, 
it being understood that the general formulas suitable 
to various crops, and the quantities ordinarily applied, 
are subject to wide variations. 

The fact that there are so many mixtures on the market 
in this country for the same crops would be rather amus- 
ing, did it not so strikingly expose the ignorance of the 
manufacturer as well as the gullibility of the public. 
Recognizing the need of standard formulas subject to 
change according to local conditions, Van Slyke ^ has 
offered the following for general use : — 



* Van Slvke, L. L. Fertilizers and Crops, p. 528. New 
York. 1912. 



572 SOILS: PROPERTIES AND MANAGEMENT 
Fertilizer Formulas for General Application 



Crops 



Leguminous 
Cereal 
Garden . . 
Grass 
Orchard 
Root . . 



Percentage 

OP N 



Percentage 
OP PjOs 



Percentage 
OF KjO 



10 
5 

10 
9 

10 

7 



While it is recognized that these formulas are probably 
far from correct in their application to such groups as 
the garden crops, where so many entirely different plants 
are concerned, it is felt that they furnish the basis, as 
far as our knowledge now extends, for a more economic 
fertilization. The variation of such mixtures to suit 
specific needs is a part of fertilizer practice. 

The carriers largely used for such readily available 
mixtures are sodium nitrate, acid phosphate, and potassium 
chloride or sulfate. Tankage or blood is often substituted 
for sodium nitrate where humus is desirable, while am- 
monium sulfate and calcium cyanamid are growing in 
popularity. Raw rock phosphate and basic slag are used 
rather largely in separate applications, the amounts 
being usually larger than with the ordinary fertilizer 
materials. 

The other phase of fertilizer practice is in the amount 
to be applied. With all the groups considered above 
except garden and root crops, the applications are rela- 
tively light, ranging from 150 to 300 pounds to an acre. 
Where excessive vegetative growth is required, as in silage, 
the rate may be increased to 500 pounds. In the top- 
dressings of meadows or grains, the rate varies from 75 



FERTILIZER PRACTICE 573 

to 150 pounds an acre. Very often this dressing is sodium 
nitrate alone. With garden and root crops the amount 
of fertilizer applied is very large, ranging from 800 to 
sometimes as high as 2000 pounds. The cropping here 
is intensive, and the expenditure for fertilization may be 
large and yet yield handsome profits. 

It must always be remembered that in fertilizer prac- 
tice the very high yields obtained under fertilizer stimu- 
lation are not always the ones that give the best returns 
on the money invested. In other words, the law of 
diminishing returns is a factor in the influence of ferti- 
lization on crop yield. This relationship is clearly shown 
by the curve illustrating the law of the minimum (par. 
469), in which the return for each increment of fertilizer 
becomes less and less as the total quantity added becomes 
greater. It is evident, therefore, that with an excessive 
application of any mixture, the returns to an increment 
will at last become so small that the increased crop fails 
entirely to pay for even the fertilizer, not to mention such 
charges as cost of application, harvesting of increased 
crop, storage, and the like. The application of moderate 
amounts of fertilizer is to be urged for all soils until the 
maximum paying dose that may be applied to any given 
crop is ascertained by careful experimentation. Over- 
fertilization probably accounts for the fact that such a 
large proportion of the fertilizers sold to the farmers each 
year not only is entirely wasted, but probably in some 
cases even becomes detrimental to crop yield. 

480. Systems of fertilization. — During the evolution 
of fertilizer practice, particularly since the early part 
of the nineteenth century, a number of systems of apply- 
ing fertilizer have been advocated or have been in actual 
use. These may be listed as follows : — 



674 SOILS : PROPERTIES AND MANAGEMENT 

1. Single-element system. — Tliis was one of tlie first 

to be suggested, and was achocated because each 
particular crop was supposed at that time to 
respond largely to one element. Thus, nitrogen 
was supposed to dominate wheat, rye, and oats ; 
phosi)horic acid, to dominate corn, turnips, and 
sorghum ; and potash to dominate potatoes, 
clover, and beans. Present knowledge of the 
balancing effects of fertilizers shows this idea to 
be fallacious. 

2. Abundant suppJij of minerals. — This system had 

its origin from the fact that potash and phosphoric 
acid are relatively cheap and are slowly leached 
from the soil, while nitrogen is expensive and easily 
lost. Such a plan, therefore, provides always plenty 
of potash and phosphorus, which is to be balanced 
each season with sufficient nitrogen to give paying 
yields. 

3. A system based on the plant-food taken out by the 

crop. — According to this plan, as much plant- 
food is added each year as will probably be taken 
out by the plant, this being determined by chemi- 
cal analyses. This system overlooks the fact 
not only that difi'erent plants feed difi'erently on 
the same soil, but that the same crop exhibits 
marked variability with change of season and 
change of soil. ]Moreover, no allowance is made 
for losses by leaching, which are known to equal 
at times the losses due to plant growtli. 

4. Irrational system. — This is the plan followed l)y 

many farmers where fertilizers are an important fac- 
tor in soil management. The formula is changed 
from year to year, in a vain attempt to strike a 



FERTILIZER PRACTICE 575 

hif^h point in production. The same continual shift 
is found in the ([uantities applied. Too often 
the specific brand used is determined by the trade 
name that it carries or l)y the recommendation of 
the retail merchant, rather than from a careful 
consideration of the guarantee or of the carriers 
for each important element. The educational 
phase of home mixing should do much to eliminate 
this system. 
5. Fertilization of the money crop. — In trucking or in 
general farming operations one crop is usually a 
money crop. Naturally its stimulation by heavy 
fertilization will pay better than applications to 
crops that bring less on the market. The general 
plan in this system is to allow the crops following 
the money crop to utilize the residuum. When 
this residual influence works out, the system is 
likely to be a profitable one ; but when the follow- 
ing crops fail to respond, the method becomes 
wasteful in the extreme. 

In the selection of a system that will result in an ef- 
fective utilization of fertilizers, only two of the plans de- 
scribed above need be considered. In any fertilizer, 
phosphoric acid and potash should always be present in 
amounts sufficient to more than balance the nitrogen, 
since the activity of nitrogen is so pronounced. There- 
fore a scheme that calls for an abundance of minerals is 
a sound one. This, coupled with the heavy fertilization 
of the money crop, does not, however, constitute what 
might be considered a rational system, since the crops 
that follow may or may not be adequately supplied with 
plant-food. Unwise fertilization often leaves the soil. 



676 SOILS: PROPERTIES AND MANAGEMENT 

as far as its balance is concerned, less able to yield a 
paying crop than })efore. The careful fertilization of the 
rotation, then, with special attention to the money crop, 
is the only rational system that can ordinarily be employed, 
since it not only cares for the crop on the land but also 
looks to those that are to succeed. The attention that 
must necessarily be paid to the fertility of the soil in such 
a system insures the establishment of a soil management 
which will ultimately result in a great conservation of 
fertility, while at the same time raising the yields and 
increasing the prosperity of the farming class. 



CHAPTER XXVI 
FARM MANURES 

Of all the by-products of the farm, barnyard manure 
is probably the most important, since it affords a means 
whereby the unused portion of the crop, the residue of 
the finished farm product, may again be returned to the 
soil. This country is now entering on an era in which 
the prevention of all waste is becoming more and more 
necessary and a nearer approach to a self-sustaining sys- 
tem of agriculture far more essential. A clear under- 
standing of the composition of farm manure, the changes 
it undergoes, and its avenues of loss, and also of methods 
for its practical handling, and a realization of its effects 
both on soil and on crop, are of vital importance. This 
need appeals not only to the practical man but to the 
theoretical and technical man as well, for here is a field 
in which theory and practice not only meet but widely 
overlap. 

481. General character and function of farm manures. 
— The term farm manure ma>' be employed in reference to 
the refuse from all annuals of the farm, although, as a 
general rule, the bulk of the ordinary manure which ul- 
timately finds its way back to the land is produced by 
cattle and horses. This arises not only because these 
animals consume the greater part of the grain and rough- 
age on the average farm, but also because the methods 
of handling them make it easier and more practicable to 
2p 577 



578 SOILS: PROPERTIES AND MANAGEMENT 

conserve their excreta. Yard manure generally refers 
to mixed manures. The mixing usually occurs during 
storage, either for convenience in handling or for the pur- 
pose of checking losses and facilitating fermentation. 
Thus, horse and cow manures are commonly mixed, since 
the too rapid fermentation and probable loss of ammonia 
in the former is checked, while at the same time a more 
rapid and much more complete decay is encouraged in 
the latter. 

The ordinary manure consists of two original compo- 
nents, the solid and the liquid portion. As these con- 
stituents tlift'er greatly, not only in composition but also 
in physical properties, their proportions must appreciably 
affect the quality of the excreta and its agricultural \'alue. 
Litter added for bedding or for adsorptive purposes is 
almost always an important factor, for while it prevents 
losses of the soluble constituents it may at the same time 
lower the value of the product for a unit amount. 

Farm manure ordinarily fulfills two functions which 
are usually not so simultaneously yet clearly developed 
in any other material — that of a direct and that of an 
indirect fertilizer. Consisting of 73 per cent of water 
and only 27 per cent of dry matter, the percentages of 
plant-food are necessarily low. As mixed farm manure 
contains on the average ^ 0.50 per cent of nitrogen, 0.25 
per cent of phosphoric acid, and 0.60 per cent of potash, 
considerable quantities of plant-food elements are added 
in an ordinary application. Ten tons of average manure, 
even if only one-half of the nitrogen, one-sLxth of the 
phosphorus, and one-half of the potash are readily avail- 
able, is equivalent to 300 i)()unds of sodium nitrate, GO 

1 Sec Analyses, Storer F. II. Agriculture, pp. 237-248. 
New York. 1910. 



FARM MANURES 579 

pounds of acid phosphate, and 125 pounds of potassium 
chloride. This is equivalent to the addition of 485 
pounds of an approximately 10-2-12 ready-mixed ferti- 
Hzer. Moreover, from the fact that so large an amount 
of the plant-food carried is not readily available, it acts 
as a residuum, which is slowly given up to the succeeding 
crops. It has been shown in England ^ that paying in- 
creased returns may be obtained from manure four years 
after its application. At Rothamsted, England,- a 
residual impetus was noticeable on crops forty years after 
the soil was manured. This, however, is an exceptional 
case. 

Farm manure may act as an indirect fertilizer in its 
tendency toward improved physical relations. The addi- 
tion of organic matter is the vital factor here. Better 
tilth, better aeration, improved drainage, and increased 
water capacity are the necessary accessories to a rise in 
humus content. The influence of manure on the avail- 
ability of the mineral constituents of the soil is not the 
least of its indirect effects. Even the increased adsorp- 
tive power of the soil should be mentioned, in its tendency 
toward the counteraction of toxic principles. 

Another general characteristic of average farm manure 
is that, while it is a fertilizer, it is an unbalanced one. 
Proportional very roughly to a 10-2-12 commercial mix- 
ture, any one acquainted with general fertilizer practice 
can see that it is too high in nitrogen and too low in avail- 
able phosphoric acid. The elimination of such a condi- 

1 Voelcker, J. A., and Hall, A. D. The Valuation of Unex- 
hausted Manure Obtained by the Consumption of Foods by 
Stock. London. 1903. 

2 Hall, A. D. Fertilizers and Manures, p. 213. New York. 
1910. 



580 SOILS: PROPERTIES AND MANAGEMENT 

tion and a balancing thereby of the plant ration is one 
of the many problems that present themselves in the 
economic handling and utilization of animal residues. 

482. Variable composition of manures. — The manure 
produced on an a\erage farm is rather likely to vary 
markedly in composition and character from time to 
time. It may even change radically from one day to 
another. There are five general factors that are usually 
listed as being responsible for this variation: (1) litter; 
(2) class of animal ; (3) individuality, condition, and age of 
animal ; (4) food of animal ; and (5) handling of manure. 

483. Litter. — Perhaps under ordinary circumstances 
the amount and character of the litter has as much to 
do with the variation in manurial composition as has 
any other one factor, if not more. By an increase in 
the amount of bedding, the product becomes bulky, 
light in weight, and difficult to handle. This is likely 
to be the case with manure from livery stables, where 
the litter is used to keep the horses clean and not for 
purposes of plant-food conservation. That bedding must 
also exert a marked effect on chemical composition is 
evident from the following analyses : — 

Composition op Litter 





N 


P2OS 


K2O 


Sawdust shavings .... 


0.10 


0.20 


0.40 


Oat straw 


0.62 


0.20 


1.04 


Peat 


2.63 


0.20 


0.17 


Leaves 


0.65 


0.15 


0.30 



Sawdust and shavings add little of value to the manure 
and really act as a diluent. While they are good absorb- 



FARM MANURES 



581 



ents they decompose so slowly as to make them somewhat 
objectionable on light soils. Leaves decompose readily, 
but add little fertility. Oat straw carries no more nitro- 
gen than does average manure, and this nitrogen, like 
that of peat or muck, is not readily available as plant- 
food. Litter, however, is of such extreme importance as 
an adsorbent that the resistant qualities of even such 
materials as shavings can be to a degree ignored. Be- 
cause of the influence of the bedding on composition, 
manure should never be bought unless this phase has 
been carefully looked into. 

484. Class of animal. — The second factor causing 
radical variation in the composition of farm manure is 
the class of animal by which it is produced. The following 
figures,^ compiled from Ohio, Connecticut, and New York 
(at Cornell University), illustrate this point clearly: — 





Percentage of 




H2O 


N 


P 


K 


Horse manure with straw 
Cow manure with straw 


62.80 
78.00 


0.57 
0.46 


0.12 
0.13 


0.54 
0.36 



A working horse on maintenance ration will return in 
the manure almost all the nitrogen and minerals taken 
as food. In other words, the building-up and the break- 
ing-down, or elimination, processes are about equal. 
A young fattening pig, on the other hand, will return only 
about 85 per cent of the nitrogen received as food and 96 
per cent of the mineral material, and a milking cow 75 
per cent and 89 per cent, respectively. 

1 Thorne, C. E. Farm Manures, p. 89. New York. 1914. 



582 SOILS: PROPERTIES AND MANAGEMENT 



485. Individuality, condition, and age of animal. — 

\'ari()us animals dilVer in ca])a('ity, some rctaininij much 
more of the elements eontained in the food than <h) others, 
and consequently producing a poorer manure. The 
service to which the animal is subjected is also a factor. 
A milch cow will certainly utilize more nutrhnents than 
an animal not in that condition. Age is perhaps more 
accountable for variation in farm mamire tlian either of 
the other two causes. A young animal gaining in muscle 
and bone is storing away large quantities of nitrogen, 
phosphorus, and potash, and producing a manure corre- 
spondingly poorer in these ingredients. 

486. Food of animal. — Since the animal will retain 
only a certain (quantity of tlie food elements, it is reason- 
able to suppose that the richer the food, the richer will 
be the corresponding excrement, both liquid and solid. 
Such has proved to be the case. Wheeler,' in studying 
the rations of chickens, found the following dilference 
in the manure produced : — 



Ration 


Percentage of 


HsO 


N 


P 


K 


Fresh hen manure (nitrog- 
enous ration) . . . 

Fresh hen manure (car- 
bonaceous ration) . . 


59.7 
55.3 


0.80 
0.G6 


0.41 
0.32 


0.27 
0.21 



From Ohio,2 where the production of manure has been 
most thoroughly investigated, the following data may be 
quoted : — 

1 Wheeler, W. P. Poultry Feeding Experiments. Kept. 
New York (Geneva) Agr. Exp. Sta., No. 8, p. 02. 1889. 

- Thorne, C. E., and others. The Maintenance of Fertihty. 
Ohio Agr. Exp. Sta., Bui. 183. 1907. 



FARM MANURES 



583 



Effect of Ration on Manurial Composition 





Percentage op 




N 


P 


K 


Corn and mixed hay . . . 
Corn, oil meal, and hay 
Corn, oil meal, and clover 


1.49 
1.55 
1.68 


0.23 
0.24 
0.26 


1.11 
1.02 
1.04 



487. Handling manure. — In dealing with a product 
of which ahnost one-half is liquid, there is great danger 
that a considerable amount of valuable plant-food will be 
lost by leaching. The modification and consequent 
lowering of the plant-food value of farm manure is a 
vital question in the economic handling of this product. 
Next to the litter, lack of care is perhaps the most im- 
portant single factor concerned in altering the chemical 
composition of manures in general. The influence of 
handling is so clearly brought out by the following figures 
from Scliutt/ on mixed horse and cow manure, that further 
discussion seems unnecessary. The protected manure in 
this case was in a bin under a shed. The exposed sample 
was in a similar bin but unprotected from the weather : — 



Loss of organic matter 
Loss of nitrogen . 
Loss of phosphoric acid 
Loss of potash . . . 



Loss AT End of 
Six Months 
(Percentage) 



Protected Exposed 



58 

19 



3 



65 
30 
12 

29 



Loss AT End of 

Twelve Months 

(Percentage) 



Protected Exposed 



60 

23 

4 

3 



69 
40 
16 
36 



* Sehutt, M. A. Barnyard Manure. Canadian Dept. Agr., 
Centr. Exp. Farm, Bui. 31. 1898. 



584 SOILS: PROPERTIES AND MANAGEMENT 



488. Composition and character of farm manures. — 

Although the probable composition of farm manures is so 
difficult to state in exact figures, compilations of the 
available data have yielded percentages which, while 
they demand a most liberal interpretation, afford con- 
siderable light regarding the differences that normally 
exist between the excrement of various animals. Of 
these compilations, Van Slyke's is perhaps the best. 

The Composition of Fresh Manure ^ 



Excrement 


Percentage op 


H2O 


N 


P2O6 


K2O 


Solid 80 per cent 


75 


0.55 


0.30 


0.40 


Horse Liquid 20 per cent 


90 


L35 


Trace 


1.25 


Whole manure 


78 


0.70 


0.25 


0.55 


[ Solid 70 per cent 


85 


0.40 


0.20 


0.10 


Cow { Liquid 30 per cent 


92 


1.00 


Trace 


1.35 


[whole manure 


86 


0.60 


0.15 


0.45 


f Solid 67 per cent 


60 


0.75 


0.50 


0.45 


Sheep Liquid 33 per cent 


85 


L35 


0.05 


2.10 


[ Whole manure 


• 68 


0.95 


0.35 


1.00 


[ Solid 60 per cent 


80 


0.55 


0.50 


0.40 


Swine Liquid 40 per cent 


97 


0.40 


0.10 


0.45 


Whole manure 


87 


0.50 


0.35 


0.40 



Since the horse does not ruminate its food, the manure 
is likely to be of an open character. It is also a fairly 
dry manure, as is that from sheep, the liquid in these two 
manures making up 20 and 33 per cent, respectively, 
of the whole product. The complete manure from these 
two animals contains 78 and 68 per cent, respectively. 



1 Van Slvke, L. L. 
York. 1912. 



Fertilizers and Crops, p. 291. New 



FARM MANURES 585 

of water — a considerable contrast to the 86 and 87 per 
cent presented by the cattle and swine excrements. 
Cattle and swine manures, being very wet, are rather 
solid and compact. The air, therefore, is likely to be 
excluded to a large degree and decomposition is relatively 
slow. They are usually spoken of as cold, inert manures 
as compared with the dry, open, rapidly heating excre- 
ments obtained from the horse and the sheep. 

In every case except that of swine the liquid portion 
of the various excrements is much the richer in nitrogen, 
containing on the average more than twice as much when 
compared on the percentage basis. The liquid is also 
richer in potash than the solid, averaging for the four 
classes of animals 1.36 per cent as compared to 0.34 per 
cent contained in the solid manure. Most of the phos- 
phoric acid, however, is contained in the solid excrement, 
only traces being found in the urine except in the case 
of the swine. It is therefore evident that the liquid 
manure, pound for pound, is more valuable in so far as 
the plant-food elements are concerned. The advantage 
leans heavily toward the urine also in that the constit- 
uents therein contained are immediately available ; this 
cannot be said of the solid manure. 

489. Actual plant-food in liquid and solid excrement. — 
While the liquid manure carries more nutriments to an 
equal weight than the solid, it yet remains to be seen 
which actually carries more of the primary food elements. 
In general, more solid manure is excreted than liquid, 
tending to throw the advantage toward the former in so 
far as total food elements are concerned. The following 
table, adopted from Van Slyke,^ bears on this point : — 

* Van Slyke, L. L. Fertilizers and Crops, p. 295. New 
York. 1912. 



586 SOILS: PROPERTIES AND MANAGEMENT 



Distribution of Plant-Pood Constituents between the 
Liquid and the Solid of Whole Manure 



Excrement 


Percentage 
OP Total 

Nitrogen 


Percentage 

OP Total 

Phosphoric 

Acid 


Percentage 

OF Total 

Potash 




Solid 


Liquid 


Solid 


Liquid 


Solid 


Liquid 


Horse 

Cow 

Sheep 

Swine 


62 
49 
52 
67 


38 
51 

48 
33 


100 

100 

95 

88 






5 

12 


56 
15 
30 
57 


44 
85 
70 
43 


Average 

Average for horse and 
cow 


57 
55 


43 
45 


95 
100 


5 



40 
35 


60 
65 



It is seen here that a httle more than one-half the 
nitrogen, ahnost all the phosphoric acid, antl about 
two-fifths of the potash, are found in the solid manure. 
Nevertheless this apparent advantage of the solid manure 
is balanced by the ready availability of the constituents 
carried by the urine, giving it in total about an equal 
commercial and agricultural value with the solid excre- 
ment. Such figures are suggesti^■e of the care that should 
be taken of the liquid manure. Its ready loss of nitrogen 
by fermentation, and the ease with which all its valuable 
constituents may escape by leaching, should make it 
an object of especial regard in handling. 

490. Production of manure. — A well-fed, moderately 
worked horse will produce daily from 45 to 3r) pounds 
of manure, of which from 10 to 11 pounds is urine. A 
cow, on the other hand, having a greater food capacity, 
will excrete from 70 to 90 pounds during the same period, 
of which from 20 to 30 pounds is liquid. Swine and 



FARM MANURES 



587 



sheep, varying so greatly in weight, will excrete such 
widely different quantities that it is difficult and mis- 
leatling to express the amount based on the individual. 
A clearer method of comparison is that employed below, 
in which a thousand pounds in weight of animal is made 
the basis of the calculation : — 

Manure Excreted by Various Farm Animals to the 1000 
Pounds Live Weight 



Animal 


Pounds 
A Day 


Tons a 
Year 


Horse ' 


50 
70 
40 
85 
34 


9.1 


Cow - 


12.7 


Steer •* 


7.3 


Swine * 


15.5 


Sheep ^ 


6.2 







It is quite evident that, for the weight of animal, the 
swine and the cow give the heaviest production of manure 
on the farm, but it should be remembered also that they 
consume the greatest amount of food. Whether these 
animals are the most economical in production of manure 
must depend largely on age and individuality. 

' Roberts, I. P., and Wing, H. H. On the Deterioration of 
Farmyard Manure by T^eaching and Fermentation. Cornell 
Univ. Agr. Exp. Sta., Bui. 13. 1889. Also, Roberts, I. P. 
The Production and Care of Farm Manure. Cornell Univ. 
Agr. Exp. Sta., Bui. 27. 1891. Also, Watson, G. C. The 
Production of Manure. Cornell Univ. Agr. Exp. Sta., Bui. 56. 
1893. 

- Thorne, C. E. Farm Manures, p. 97. New York. 1914. 

5 Thorne, C. E., and others. The Maintenance of Fertility. 
Ohio Agr. Exp. Sta., Bui. 183. 1907. 

* Watson, G. C. The Production of Manure. Cornell Univ. 
Agr. Exp. Sta., Bui. 56. 1893. 

^ Van Slvke, L. L. Fertilizers and Crops, p. 294. New 
York. 1912. 



588 SOILS: PROPERTIES AND MANAGEMENT 

491. Heiden's formulas. — Perhaps a better and more 
nearly accurate means of calculatino; the prol)ahle pro- 
duction of manure is from the food consumed, rather 
than from the combined weight of animals kept. Formu- 
las have been devised from experimental data in Ger- 
many and are designated as Heiden's formulas.' From 
the amount of absolute dry matter fed and the excrement 
produced, Heiden was able to determine certain definite 
relationships of the latter to the former. These, of course, 
varied for different animals, being 2.10 for the horse, 3.80 
for the cow, and 1.80 for sheep. For example, if a horse 
received 20 pounds of dry matter daily, the manurial 
production would be 42 pounds. Such formulas are of 
particular value on English farms, where the incoming 
renter must pay the preceding tenant for the manure 
produced on the farm during ])revious years. 

492. Poultry manure. — The excrement from poultry 
is extremely variable, due to causes that have already 
been discussed. In general, this manure is much richer 
than that from other farm animals. Storer - cites the 
following analysis : — 

Composition of Poultry Manure 

Per cent 

Water 0.56 

Nitrogen . . 1.60 

Phosphoric acid 1 .75 

Potash 0.90 

Lime 2.25 

' Henry, W. A. Feeds and Feeding, p. 265. Madison, 
Wisconsin. 1904. 

"^ Storer, F. IT. Agriculture, Vol. 1, p. 613. New York. 
1910. Also, Vorhees, E. B. Ground Bono and Miscellaneous 
Samples. New Jersey Agr. Exp. Sta., Bui. 84. 1891. Also, 



FARM MANURES 589 

It is evident that poultry excrement is the most vahi- 
able manure produced on the farm. It dries readily 
and the loss of nitrogen by fermentation is not great. 
Because of its great strength farmers are verv' careful 
regarding its application, as injurious effects on the crop 
may result. Notwithstanding its great value it probably 
receives less care than any other manure produced on the 
farm. 

493. Commercial and agricultural evaluation of 
manures. — For purposes of comparison, experimenta- 
tion, and sale, farm manures are often evaluated in a way 
similar to that used with commercial fertilizers. The 
great difficulty here lies in arriving at prices for the im- 
portant constituents which are at all comparable with the 
value of the manure in the field. The following figures 
are calculated from the preceding tables, and show not 
only the comparative value of the fresh excrement from 
different sources but also what might be considered as 
fair prices a ton for the manures. The value of the nitro- 
gen is here placed at ten cents a pound, the phosphoric 
acid at two and one-half cents, and the potash at four 
cents : — 

Value of 

manure 

a ton 

Swine manure $1.50 

Cow manure 1.64 

Horse manure 1.97 

Sheep manure 2.87 

Poultry manure 4.80 

Average of cow manure and horse manure mixed . 1.80 

Coessman, C. A. Massachusetts State Exp. Sta., Bui. 37, 
1890, and Bui. 63. 1896. 



590 SOILS: PROPERTIES AND MANAGEMENT 

This commercial evaluation, of course, must be applied 
with care because of the many factors tending to vary 
the composition of the excrement. Litter, particularly, 
will exert a great influence in this direction. Perhaps a 
safe figure as regards the commercial value of manure 
as it is likely to be handled on the average farm is about 
$1.50 a ton. This approaches more nearly the price that a 
market gardener, for example, may pay for such a j)roduct. 

This commercial evaluation must never become con- 
fused with what is known as the agricultural value of a 
manure. The former is based on composition, while 
the latter arises from the effects as measured in crop 
growth. A manure of high commercial value may, when 
placed on the soil, yield only a low to medium agricultural 
return. This latter evaluation is, of course, the one of 
greatest significance in agricultural practice. A very 
good example of this might be cited from the Ohio experi- 
ments ^ with manure. In this case both treated and 
untreated manures were evaluated commercially and 
were then applied to the land. The value of the increased 
crops in a three-years' rotation was then calculated in 
terms of return to a ton of manure applied : — 

Commercial and Agricultural Evaluation of Manures 



Manure 


Commer- 
cial Value 


Agricul- 
tural 
Value 


Yard manure untreated 

Yard manure plus floats 

Yard manure plus acid phosphate . . . 

Yard manure plus kainit 

Yard manure plus gypsum 


$1.41 
2.04 
1.65 
1.45 
1.48 


$2.15 
3.31 
3.67 
2.79 
2.76 



' Thorne, C. E., and others. The Maintenance of Fertility. 
Ohio Agr. Exp. Sta., Bui. 183, pp. 206-209. 1907. 



FARM MANURES 591 

In practice, then, it is this agricultural evaluation which 
must be especially watched. Its expression should be 
not only in net yield to the acre, but also in net return 
to a ton of manure applied. 

494. The fermentation of manure.^ — During the 
processes of digestion the food of animals becomes more 
or less decomposed and decayed. This condition comes 
about partly because of the digestive processes and 
partly from the bacterial action that takes place, largely 
in the lower intestines. Of these two influences within 
the animal, bacterial activities are probably of the greater 
importance as far as the breaking-up of the complicated 
foodstuff's is concerned. The fresh excrement, then, as 
it comes from the stable, consists of decayed or partially 
decayed plant materials, with a certain amount of broken- 
down animal tissue and mucus. This is more or les# 
intimately mixed with litter and the whole mass is wetted, 
or moistened, with the liquid excrement, carrying, as it 
does, considerable quantities of soluble nitrogen and 
potash. This mass of material, ranging from the most 
complex compounds to the most simple, is teeming with 
bacteria, especially those that function in decay and putre- 
faction. The number very often runs into billions to a 
gram of excrement. In such an environment it is of 
little wonder that biological changes go on so rapidly. 

Altliough so many different groups of organisms live 
and function in manure, and although so many products, 
both simple and complex, are continually being split 
off, for convenience and simplicity the bacteria may be 

1 Good discussions may b? found as follows : Lipmau, J. G. 
Bacteria in Relation to Country Life, pp. 30.'{-35(). New York. 
1911. Hall, A. D. Manures and Fertilizers, pp. 184-210. 
New York. 1910. 



592 SOILS: PROPERTIES AND MANAGEMENT 

grouped under two heads, aerobic and anaerobic. The 
former work in the presence of oxygen, the latter when 
air is either lacking or only very slightly present. This 
grouping is not a distinct one by any means, as many 
organisms may function not only in air but also when 
oxygen is lacking. The products, however, are as dif- 
ferent under these two conditions as if they arose from 
distinct organisms. 

495. Aerobic action. — When manure is first produced 
it is likely to be rather loose, and if allowed to dry at 
once it becomes well aerated. The first bacterial action 
is therefore likely to be rather largely aerobic in nature. 
Transformations are very ra])id and are accompanied by 
considerable heat, ranging from 100° to 150° F. and some- 
times higher. This action falls largely on the simple 
tiitrogenous compounds. Urea is principally aflFected, 
and will very quickly disappear from well-aerated manure. 
The reaction is as follows : — 

COXN2H4 + 2 H2O = (XH4)2 CO3 

The ammonium carbonate is a volatile compound, and 
on the least exposure and evaporation of the manurial 
liquids it changes into ammonia and carbon dioxide. 
Thus nitrogen may be rapidly lost from manure by the 
unwise allowing of excessive aerobic decay and decom- 
position to proceed. 

This complex group of aerobic putrefactive organisms 
also attack to a certain extent the more complicated ni- 
trogenous compounds, as well as some of the simpler car- 
bohydrates contained in the solid and the liquid portions 
of the manure. More carbon dioxide therefore results, 
as well as certain simplified products which ultimately 
may be reduced to such a form as to be a\ailable as plant- 



FARM MANURES 598 

food. In other words, the whole mass of the manure 
tends to simpler forms. The mass becomes decayed, 
humus is produced, and available plant-food is evolved. 

496. Anaerobic action. — As the manure becomes 
compacted, especially if it is left moist, oxygen is grad- 
ually excluded within the heap and its place is taken by 
carbon dioxide, which is given oflf during the process of 
any form of bacterial activity. The fermentation now 
changes from aerobic to anaerobic, it becomes slower, and 
the temperature falls to as low as 80° or 90° F. New 
organisms ma}' now function, and even some of the same 
ones that were active under aerobic conditions may con- 
tinue to be effective. The process is now a deep-seated 
one and the products become changed to a considerable 
degree. Carbon dioxide, of course, continues to be evolved, 
but instead of ammonia being formed the nitrogenous 
matter is converted into the usual putrefactive products, 
such as indol, skatol, and the like. The carbonaceous 
matter is resolved into lunnerous hydrocarbons, of which 
methane (CH4) is prominent ; and as a by-product of 
the breaking-down of the proteins, hydrogen sulfide 
(H2S) and sulfur dioxide (SO2) are evolved. The com- 
plex nitrogenous and carbohydrate bodies are attacked 
with the splitting-off, not only of simpler materials, but 
often of those more complex. Such compounds may be 
listed in general as organic acids and humic bodies. 
They of course ultimately succumb to simplification. 

497. Fermentation in general. — In any process of 
fermentation, acids tend to form which if not neutralized 
will render the mass acid and impede bacterial activity. 
This occurs when the solid excrement decomposes alone. 
The liquid manure, however, is alkaline and will tend 
to correct any acidity due to fermentation. The advan- 

2q 



594 SOILS: PROPERTIES AND MANAGEMENT 

tage of eitlier Iia lulling the liquid and the solid together, 
or pumping the liquid over the solid at intervals, is there- 
fore apparent. 

The general changes in any manure pile can readily 
be recapitulated. First is the aerobic action, with escape 
of ammonia and carbon dioxide. Next the manure is 
wetted, it compacts, and the slow, deep-seated decay 
sets in with a simplification of some compounds, with 
the production of acids, and with a gradual formation 
of humic materials. As the manure becomes alternately 
wet and dry, the two general processes may follow each, 
other in rapid succession, the anaerobic bacteria attack- 
ing the complex materials, the aerobic affecting both the 
complex and the simpler compounds. Carbon dioxide 
is given off continuously during the process. 

498. Gases from manure. — The changes in the 
composition of the gases drawn from wet and compact 
manure, as compared with those from the same pile dry 
and open, are well shown from results by Deherain.^ 
The pile in this experiment was about eight feet high : — 

Composition of Gases from Dry and Moist Manure 





Percentage op 




COj 


O2 


CH4 


N 


[Top 

Dry manure < Middle 

[Bottom 

Wet and [ Top 

compact < Middle 

manure [ Bottom 


7.2 
14.5 
50.8 
42.7 
49.8 
47.8 


7.0 
4.7 
0.0 
1.1 
0.0 
0.0 


0.0 
1.3 
49.2 
52.4 
48.3 
51.2 


85.8 
79.5 
0.0 
9.8 
2.2 
1.0 



1 Hall, A. D. Fertilizers and Manures, p. 188. New York. 1910. 



FARM MANURES 



595 



It is noticeable that nitrogen ceases to be lost under 
anaerobic conditions, but the production of methane is 
much increased. Carbon dioxide is present at all times, 

499. Change of bulk and composition of rotting manure. 
— Because of the great loss of carbon dioxide during the 
fermentation processes, there is a considerable change in 
bulk of the manure. Fresh excrement loses 20 per cent 
in bulk by partial rotting, 40 per cent by more thorough 
rotting, and 60 per cent by becoming completely decom- 
posed. This means that 1000 pounds of fresh manure 
may be reduced to 800, 600, or 400 pounds, according 
to the degree of change it has undergone. 

Although considerable loss of nitrogen may have oc- 
curred through aerobic bacterial action, and although 
both nitrogen and the minerals may have been consider- 
ably leached away, the loss of carbon dioxide is so much 
greater that generally there is an actual percentage in- 
crease of the former constituents in the well-rotted prod- 
uct. This relationship is well shown by figures from 
Wolff,^ in which the samples were compared on the basis 
of equal amounts of dry matter : — 



Composition 


OF Fresh and D 


EcoMPosED Manure 




Fresh 
(Per cent) 


Rotted 
(Per cent) 


Ash 


3.81 
0.39 
0.45 
0.49 
0.12 
0.18 
0.10 


4.76 


Nitrogen 


0.49 


Potash 


0.56 


Lime 


0.61 


Magnesia 


0.15 


Phosphoric acid 
Sulfuric acid 






0.23 






0.13 











1 Aiknian, C. M. Manures and Manuring, p. 288. 
burgh and London, 1910. 



Edin- 



596 SOILS: PROPERTIES AND MANAGEMENT 

It must be remembered, however, that this is only a 
general case and holds good only when the manure has 
had fairly careful attention. When the manure has been 
improperly handled, the soluble constituents may be lost 
as soon as formed and a rotted product may result which 
is very low in nitrogen, potassium, and phosphorus. It is 
therefore evident that the handling of the fresh manure is 
a controlling factor in the ultimate value of the product. 

A further insight into the condition of rotted manure 
is given by Voelcker,^ the data being calculated to a dry- 
weight basis : — 



Fresh 
Manure 
(Per cent) 



Rotted 
Manure 
(Per cent) 



Soluble organic matter 7.33 

Soluble inorganic matter 4.55 

Insoluble organic matter 76.14 

Insoluble inorganic matter 11.98 



15.09 

5.98 
51.34 
27.59 



These figures show the increased soluble matter in 
well decomposed manure and emphasize the value of 
rotting. The great loss of organic matter through the 
giving-off of carbon dioxide is also evident. 

500. Fire-fanging of manure. — A change of a fermenta- 
tive nature which sometimes takes place in loose and well- 
dried manure is fire-fanging. i\Iany farmers consider 
this to be due to actual combustion, as the manure is very 
light in weight and has every appearance of being burned. 
This condition, however, is produced by fungi instead 
of bacteria, and the dry and dusty appearance of the 



1 Halligan. J. R. 
ton, Pennsylvania. 



Soil Fertility and PVrtilizers. p. 
1912. 



G7. Eas- 



FARM MANURES 



597 



manure is due to the mycelium, which penetrates in all 
directions and uses up the valuable constituents. jManure 
thus affected is of little value either as plant-food or as a 
soil amendment. 

501. Waste of farm manures. — iVny system of agri- 
culture, in order to be permanent, must arrange for the 
addition of as much plant-food as is removed in the crop 
and the drainage water combined. Even if all of the 
crop were returned to the soil, a permanent system of 
agriculture would fall far short of being established, since 
at least as much plant-food is removed by leaching as by 
cropping. As a matter of fact, it is not even possible to 
return to the land as farm manure all the constituents 
taken off in the crop, due to the ease with which loss occurs. 
These losses may be grouped under two general heads: 
(1) those that occur as the food passes through the animal ; 
and (2) those that are due to leaching and fermentation. 

502. Losses due to digestion. — A certain quantity of 
material is necessarily taken from the original food as it 
passes through the animal. This loss falls most heavily 
on the organic matter and only slightly on the mineral 
constituents. Wolff ^ presents the following figures aver- 
aged from all classes of animals : — 



Percentage of Original Food Constituents Recovered 
IN Fresh Manure 





Solid 
Manure 


Liquid 
Manure 


Total 


Organic matter . . . 

Nitrogen 

Minerals 


42.5 
40.1 
59.7 


3.4 
47.2 
39.0 


45.9 

87.3 
98.7 





> Aikman, C. M. Manures and Manuring, pp. 228 and 232. 
Fidinburgh and London. 1910. 



598 SOILS: PROPERTIES AND MANAGEMENT 

It is to be noted that the or<;;anic matter of the food 
has sustained an average loss of about 55 per cent, while 
the loss of nitrogen and of minerals has been 13 per cent 
and 2 per cent, respectively. The loss of the organic 
matter is especially serious, although it can be replaced by 
using green manures and the practicing of a proper rotation. 
The loss of nitrogen can be replaced only by the growing 
of legumes or by the addition of a nitrogenous fertilizer. 

503. Losses due to leaching and fermentation. — As 
about one-half of the nitrogen and two-thirds of the potash 
in farm manures is in a soluble condition, the possibility 
of loss by leaching is very great, especially where the 
manure is exposed to heavy rainfall. The loss of phos- 
phorus is also of some consequence. In addition, the 
fermentation, especially that of an aerobic nature, will 
cause the formation of ammonia, which may be lost in 
large quantities if steps are not taken to control such 
action. It is evident that losses by leaching may be 
checked considerably by protecting the manures from 
excessive rainfall and by providing tight floors in the 
stable or an impervious bottom in the manure pit or 
under the manure pile. Packing and moistening the 
manure will change the aerobic fermentation to anaerobic, 
thus reducing very markedly the production of ammonia 
while allowing a simplification of the manurial compounds 
to proceed steadily. All wise methods of handling and 
storing manures provide against these losses through 
leaching and fermentation by protecting the manure from 
rain and by controlling fermentation through moisten- 
ing and compacting. 

It is very difficult, in quoting figures for waste of 
manure, to separate the losses due to leaching from those 
due to fermentation. The two processes go on simul- 



FARM MANURES 



599 



taneously, and the loss from one source is dependent, to 
a certain extent, on the other. It is only the nitrogen, 
however, that may be lost by both fermentation and 
leaching, the minerals being wasted only through the 
latter avenue. A few figures regarding the losses to 
manures when exposed to atmospheric conditions may 
not be amiss at this point : — 

Losses from Manure through Leaching and 
Fermentation 





New 
York' 


New 
York ' 


Canada^ 


New 
York ' 


New 
Jersey' 
(Aver- 
age for 

eight 
years) 


Ohio* 


Kind of Manure 


Horse 


Horse 


Horse 


Cow 


Cow 


Steer 


Time exposed (days) 

Loss of nitrogen (per- 
centage) .... 

Loss of phosphoric acid 
(percentage) . . . 

Loss of potash (percent- 
age) 


183 
36 
50 

60 


183 
60 

47 
76 


274 
40 
16 
34 


183 
41 
19 

8 


77 
31 
19 
43 


91 
30 
23 
58 



It seems evident that when manure is exposed to at- 
mospheric agencies, even under the best conditions, the 
losses of nitrogen, phosphoric acid, and potash will be 
on the average 45, 30, and 50 per cent, respectively. 

• Roberts, I. P., and Wing, H. H. On the Deterioration 
of Farmyard Manure by Leaching and Fermentation. Cornell 
Univ. Agr. P]xp. Sta., Bui. 13. 1889. 

^ Sehutt, M. A. Barnyard Manure. Canadian Dept. Agr., 
Centr. Exp. Farms, Bui. 31. 1898. 

3 Thorne, C. E. Farm Manures, p. 146. New York. 1914. 

* Thorne, C. E., and others. The Maintenance of Fertility. 
Ohio Agr. E.xp. Sta., Bui. 183. 1907. 



600 SOILS: PROPERTIES AND MANAGEMENT 

Under conditions on the average farm such losses may 
easily rise to 50 per cent of all the constituents, and prob- 
ably very much higher as regards nitrogen and j)otash. 
From one-half to three-fourths of the important elements 
contained in the original food fails to again reach the 
land. Hall,^ quoting from Woods' experiments at Cam- 
bridge, shows that about 10 per cent of the nitrogen in 
the food consumed is retained by the animal. He also 
shows that 15 per cent of nitrogen is lost during the making, 
and from 10 to 25 per cent during the storage, of the ma- 
nure, even under the best conditions. This gives a total 
loss of nitrogen amounting to from 35 to 50 per cent. If 
this is the loss under the best conditions, it can readily 
be seen that the loss on an average farm must approach 
65 or 75 per cent. 

Some idea as to separate losses from fermentation and 
leaching may be gained from data drawn from Canada.- 
In this experiment a mixture of horse dung and cow dung 
was divided. One-half was placed in a bin under a shed ; 
the other half was exposed to the weather, outside in a 
similar bin. After a year the two portions were analyzed 
and the losses computed : — 

Losses from Manure after Twelve Months 





Protected 
(Per cent) 


Unprotected 
(Per cent) 


Loss of organic matter 

Loss of nitrogen 

Loss of phosphoric acid 

Loss of potash 


60 

23 

4 

3 


69 
40 
16 
36 



1 Hall, A. D. Fertilizors and Manures, p. 198. New York. 
1910. 

^ Schutt, M. A. Barnyard Manure. Canadian Dept. Agr., 
Centr. Exp. Farm, Bui. 3i. 1898. 



FARM MANURES 601 

Evidently the losses by fermentation are very consider- 
ably augmented by exposure, especially if the rainfall 
is high. This waste not only is very considerable as 
regards the nitrogen, but is especially high as far as the 
organic matter is concerned. Such figures serve also 
to emphasize again the importance of shielding manure 
in storage from excessive rainfall. Some water is, of 
course, necessary, but too much serves only to carry 
away the materials already soluble or rendered soluble 
by fermentation. ^^ 

504. Increased value of protected manure. — From 
the previous discussion it is evfdent that a well-protected 
and carefully preserved manure will be higher in plant- 
food constituents than one not so handled. ]Moreover, 
the agricultural value of such manure will be higher. 
This is shown by actual tests from Ohio.^ Over a period 
of fourteen years, in a three-years' rotation of corn, wheat, 
and hay, a stall manure gave a yield 30 per cent higher 
than that with a yard manure, the quantities applied in 
each case being equal. In New Jersey, in comparing 
fresh manure with leached manure the former showed a 
gain in crop yield 53 per cent higher than the latter over 
a period of three years immediately following the appli- 
cation. Such figures are worthy of careful considera- 
tion by the average farmer. 

505. The money waste of manure. — To make the 
seriousness of the question of waste in manures more 
striking, the probable losses may be calculated in money 
value for the United States. The entire live stock of all 
kinds in this country may be roughly calculated as equiv- 

1 Thorne, C. E., and others. Plans and Summary Tables 
of the Experiments of the Central Farm. Ohio Agr. Exp. Sta., 
Circ. 120. 1912. 



602 soils: properties and management 

alent in manure producing capacity to about 100,000,000 
cattle, each weighing 1000 pounds. Assuming that 
each animal will produce manure to the value of S21 
a year and that the cattle are yarded for four months, 
the total value of excrement produced during the yarding 
period would be, in round numbers, 87{)(),000,000. If 
only one-third of the value of the manure is lost by mis- 
handling, an annual waste of $233,000,000 would occur. 
This is a very conservative estimate regarding the losses 
of farm manure throughout the United States. The an- 
nual sale of commercial fertilizers in this country, prob- 
ably amounting to over $100,000,000, is entirely inade- 
(luate to replace this loss. 

506. Handling of manures. ^ — The ultimate considera- 
tion in a study of farm manures comprises the best 
methods of economic handling, both as to labor and as to 
the saving of the constituents carried by the product. The 
greater the amount of plant-food that can be saved in 
the manure and returned to the land, the less will be the 
necessity of commercial sources of these elements. jNIany 
methods present themselves as being more or less effica- 
cious, but none are absolutely perfect, as losses by fer- 
mentation are bound to occur even though leaching is 
entirely prevented. Methods of handling are usually 
chosen because of their adaptability to particular cir- 
cumstances, rather than because of the exact amount 
of valuable constituents that they will conserve. 



1 Good discussions of handling farm manure are as follows: 
Hart, E. B. Getting the Most Profit from Farm Manure. 
Wisconsin Agr. Exp. Sta., Bui. 221. 1912. Beal, W. H. Barn- 
yard Manure. U. S. D. A., Farmers' Bui. 192. 1904. Roberts, 
i. P. The FertiHtv of the Land, Chapter IX, pp. 188-213. 
New York. 1904. 



FARM MANURES 603 

507. Care of manure in the stalls. — Considerable loss 
to manure occurs in the stable, due to fermentation and 
leaching. Before the litter can absorb the liquid, it 
is likely to ferment and to leach away in exceptional 
amounts. Therefore the first care is as to bedding, which 
should be chosen for its absorptive properties, its cost, 
and its cleanliness. The following table ^ expresses the 
absorptive capacity of some common litters : — 

Absorptive Power of Bedding for Water 

Per eent 

Wheat straw 220 

Oak leaves 162 

Peat 600 

Sawdust 435 

Spent tan 450 

Air-dry humous soil 50 

Dry peat moss 1300 

Muck 200 

The amount of litter to be used is determined by the 
character of the food. If the food is watery, the bedding 
should be increased. In general, the litter may amount 
to about one-third of the dry. matter of the food consumed. 
Sheep require about a pound of bedding a head, cattle 
from eight to ten pounds, and horses from six to seven 
pounds. No more litter than is necessary to keep the 
animal clean and to absorb the liquid manure should be 
used, as the excrement is thus diluted unnecessarily with 
material which often does not carry large quantities of 
fertilizing ingredients. 

1 Beal, W. H. Barnyard Manure. U. S. D. A., Farmers' 
Bui. 192. 1904. 



604 SOILS: PROPERTIES AND MANAGEMENT 

The next care is that floors shall be tight, so that free 
liquids cannot drain away but will be held in contact 
with the absorbing materials. The preserving of manures 
in stalls with tight floors has been for years a common 
method of handling dung in England. The trampling 
of the animals, and the continued addition of litter with 
the liquid and solid excrement, explain the reason for 
the success of the method. The following data, from 
Ohio,^ show the relative recovery of food elements in 
manure produced on a cement floor and on an earth floor, 
respectively. The experiment was conducted with steers 
over a period of six months. 

Recovery of Food Elements in Manure Produced 
ON Cement Floor; on Earth Floor 




Per Cent 



Nitrogen . 
Phosphorus 
Potash . 



62.4 

78.9 
78.4 



508. Hauling directly to the field. — Where it is pos- 
sible to haul directly to the field, this practice is to be 
advised, since opportunities for excessive losses by leach- 
ing and fermentation are thereby prevented. ]\Ianure 
may even be spread on frozen ground or on the top of 
snow, provided the land is fairly level and the snow is 
not too deep. This system saves time and labor, and 
when leaching does occur the soluble portions of the ma- 
nure are carried directly into the soil. 

509. Cement pit. — Very often it is not convenient 

1 Thorne, C. E. The Maintenance of Fertility. Ohio 
Agr. Exp. Sta., Bui. 183, p. 199. 1907. 



FARM MANURES 605 

nor possible, especially in certain parts of the year, to 
haul manure directly to the field. Means of storage 
must therefore be provided. Some farmers, if the amount 
of manure produced on their lands is large, find it prof- 
itable to construct manure pits of concrete. These 
storage pits are usually rectangular in shape, with a shed 
covering, and with open ends so that a team may drive 
in at one end and out at the other. In such a pit leaching 
is prevented by the covering and by the solid bottom. 
By keeping the manure carefully spread and well mois- 
tened, fermentation may proceed with a minimum loss 
of nitrogen. Some dairymen even go so far as to utilize 
a cistern, into which is shoveled both the liquid and the 
solid manure. Later, when fermentation has proceeded 
sufficiently, the material is pumped out and applied to 
the land. This method is not to be advocated in this 
country except under particular conditions. 

510. Covered barnyard. — Another method of storage 
is by means of a covered barnyard. Such a yard must 
have an impervious bottom. The manure is spread out 
in the yard, and if animals are allowed to exercise here 
the manure is kept thoroughly packed as well as damp. 
The storage of manure in deep stalls, a favorite method 
in England, is similar to this system and has been shown 
to be very economical. It also afi^ords an opportunity 
for the mixing of the manure from different classes of 
animals. The desirability of this has already been shown 
regarding horse and cow excrements. The advantages 
of trampling, as far as the keeping qualities of manure 
are concerned, are clearly shown by the following figures 
taken from the work of Frear : ^ — 

1 Frear, W. Losses of Manure. Pennsylvania Agr. Exp. 
Sta., Bui. 63. 1903. 



606 SOILS: PROPERTIES AND MANAGEMENT 
Loss OF Manure in Covered Sheds 





Percentaoe op 




N 


K2O 


PsOs 


Covered and trampled . . . 
Covered and untrampled . . 


5.7 
34.1 


5.5 

19.8 


8.5 
14.2 



Throwing manure in heaps under a shed and allowing 
hogs to work the mass over, is an economical practice so 
far as food utilization is concerned. It interferes, how- 
ever, with proper and economical packing of the manure. 
The question to be decided is whether the added food 
value of the manure overbalances the extra losses by 
fermentation incurred by the rooting of the swine. 

511. Piles outside. — Very often it is necessary to 
store manure outside, fully exposed to the weather. 
When this is the case, certain precautions must be ob- 
served. In the first place, the pile should be located on 
level ground far enough from any building so that it 
receives no extra water therefrom in times of storm. The 
earth under the pile should be slightly dished in order 
to prevent loss of excess water. If possible, the soil 
of the depression should be puddled, or, better, lined with 
cement. 

The sides of the heap should be perpendicular, so as 
to shed water readily. The manure must be kept moist 
in dry weather in order to decrease aerobic action. Each 
addition of manure should be packed in place, the fresh 
on and above the older. This allows the carbon dioxkle 
from the well-rotted dung to pervade the fresher and 
looser portions, thus quickly establishing the aerobic 



FARM MANURES 607 

conditions so essential to economic and favorable fer- 
mentation. 

Placing fresh manure in small heaps in the field to be 
spread later, is, in the first place, poor economy of labor. 
Moreover, it encourages loss by fermentation, while at 
the same time the soluble portions of the pile escape into 
the soil immediately underneath. There is thus a poor 
distribution of the essential elements of the dung, and 
when the manure is finally spread, an overfeeding of 
plants at one point and an underfeeding at another results. 
A low efficiency of the manure is thus realized. This 
method of handling manure is not to be recommended. 

512. Distribution of manure in the field. — In the 
actual application of manure to the land, certain general 
principles should always be kept in mind. In the first 
place, e\'enness of distribution is to be desired, since it 
tends to raise the efficiency of the manure by encouraging 
a more uniform plant growth. This evenness of spread- 
ing is much aided by fineness of division. Moreover, it 
is generally better, especially in diversified farming on 
medium to heavy soils, to decrease the amounts at each 
spreading and apply oftener. Thus, instead of adding 
20 tons to the acre, 10 tons would be applied and twice 
as much area covered. The applications would then 
be made oftener. A larger and quicker return in net 
crop yield per ton of manure applied would be realized. 
This has been strikingly shown by the Ohio experiments ^ 
over a test for eighteen years in a three-years rotation of 
wheat, clover, and potatoes, the manure being placed on 
the wheat and afi'ecting the clover and the potatoes as a 

1 Thorne, C. E., and others. Plans and Summary Tables 
of the Experiments at the Central Farm. Ohio Agr. Exp, 
Sta., Circ. 120, p. 108. 1912. 



608 soils: PROPEuriES and management 

residimni. The results are expressed in yield per ton of 
manure applied : — 

Yield to the To.v of Manure when Applied in 
Different Amounts 





Wheat Clover 
(Bushels) (Pounds) 


Potatoes 
(Bushels) 


4 tons to the acre .... 

8 tons to the acre .... 

16 tons to the acre .... 


8.0 177 

4.1 1 150 
2.4 99 


37.3 
19.4 
11.6 



Not only is the increased efficiency from lower appli- 
cations apparent, but a great recovery of the manurial 
fertility in the crops also results. The Ohio experiments 
have shown that in the first rotation after the manure 
is applied, a recovery may be expected from a treatment 
of 8 tons 25 to 30 per cent higher than from one of 
IG tons. 

Evenness of application and fineness of division are 
greatly facilitated by the use of a manure spreader. This 
also makes possible the uniform application of small 
amounts of manure, even as low as five or six tons to the 
acre. It is impossible to spread so sniall an amount by 
hand and obtain an even distribution. ]\Ioreover, a 
spreader lessens the labor and more than doubles the 
amount of manure one man can apply a day. When 
any quantity of manure is to be handled, a manure spreader 
will pay for itself in a season or two at the most. 

Whether manure should be plowed under or not depends 
largely on the crop on which it is used. On timothy it 
is spread as a top-dressing. Ordinarily, however, it is 
plowed under. This is particularly necessary if the 



FARM MANURES 609 

manure is long, coarse, and not well rotted. It should 
not be turned under so deep, however, as to prevent ready 
decay. If manure is fine and well decomposed, it may 
be harrowed into the surface soil. The method employed 
depends on the crop, the soil, and the condition of the 
manure. The amount to be applied varies consider- 
ably. Eight tons to the acre would be a light dressing, 
15 tons a medimn dressing, and 25 tons heavy for an 
ordinary soil. On trucking lands, however, as high as 
50 or 100 tons is often used. 

513. Reinforcement of manure. — The reinforcement 
of farm manures is designed to accomplish two things in 
the handling of this product : (1) checking loss by leaching 
and fermentation, and (2) balancing the manure and 
rendering its agricultural value higher. Four chemicals 
may be used in this reinforcement: gypsum (CaSOO, 
kainit (KCl, mostly), acid phosphate (CaH4(P04)2 + 
CaS04), and floats (raw rock phosphate, Ca3(P04)2). 

Gypsum is supposed to act on the ammonia, changing 
it to ammonium sulfate, a stable compound. It is rather 
insoluble, however, so that its action is slow. It may be 
applied in the stable or on the manure pile. The rate 
is about 100 pounds to the ton of manure. It has no 
balancing effect. 

Kainit is added to react with any ammonia that may 
be produced and also to increase the potash in the manure. 
It is soluble, and because of its caustic tendencies it must 
not come into contact with the feet of the animals. It 
must not be spread on the manure, therefore, until the 
stock has been removed. Since manure is unbalanced 
as to phosphorus, the agricultural value of this reinforce- 
ment is likely to be slight. Kainit is usually added at 
the rate of 50 pounds to the ton of manure. 
2r 



610 SOILS: PROPERTIES AND MANAGEMENT 

Acifl phosphate, when used as a reinforcing agent, is 
applied at the rate of 50 pounds to the ton of manure. 
It is sohible, and therefore becomes intimately mixed 
with the excrement. It adds phosphorus, in which 
manure is especially lacking. Its gypsum may react 
with the ammonia. Theoretically it should prevent loss 
by fermentation, as well as function as a balancing agent. 
It must not come into contact with the feet of farm ani- 
mals. 

Raw rock phosphate, or floats, is a very insoluble com- 
pound, and consequently reacts but slowly with the 
soluble constituents of manure. Carrying such a large 
percentage of phosphorus, it tends to balance the product 
and to raise its agricultural value. It is supposed that 
the intimate relationship between the phosphate and the 
decaying manure increases the a\ailability of the former 
to plants when the mixture is added to the soil. No 
increased solubility, however, as determined by chemical 
means, has ever been as definitely shown to occur (see 
par. 439). The reinforcement is usually at the rate of 
100 pounds to the ton of manure. 

514. Benefits from reinforcing. — Experimental data 
ha\e shown that these various reinforcements have no 
eflPect on the nature, function, and number of the bacterial 
flora. Their conserving influence, if any, when the ma- 
nure is exposed, must be in checking leaching and in 
preventing loss of ammonia. The following figures 
from Ohio experiments ' show how slight this conserving 
eft'ect is. The reinforcement was at the rate of 40 pounds 
to the ton : — 



' Thorne, C. E. Maintenanoe of Fertility. Ohio Agr. 
Exp. Sta., Bui. 1S3, p. 2UG. 11)07. 



FARM MANURES 



611 



Conserving Effect of Reinforcing Agents on Manure 
Exposed for Three Months 



Treatments 


Valtje op a Ton op 
Manure 


Percentage 
OP Loss 




In January 


In April 




$2.19 


$1.41 

1.48 
1.45 
2.04 
1.65 


36 


Gypsum 

Kainit 

Floats 

Acid phosphate 


2.05 
2.24 
2.81 
2.34 


38 
35 
24 
29 



It is immediately evident that kainit and gypsum do not 
conserve the manure, and, although acid phosphate and 
floats show some influence, it is slight. The principal 
benefit from reinforcing manure, if any, must therefore 
be as a balancing agent. The figures from Ohio ^ over a 
period of fourteen years in a rotation of corn, wheat, and 
hay may be taken as evidence regarding this point. 
The manure was added to the corn at the rate of 8 tons 
to the acre. The reinforcing was 40 pounds to the ton 
of manure in everv case : — 



The Reinforcing of Fresh Manure 



Treatment 


Total Net In- 
creased Value 
OF Crop to the 
Rotation 


Net Increased 

Yield to the Ton 

OF Manure 


Manure plus floats .... 
Manure plus acid phosphate 
Manure plus kainit .... 
Manure plus gypsum .... 
Manure alone 


$35.94 
38.55 
29.67 
28.48 
26.48 


$4.49 
4.82 
3.71 
3.56 
3.31 



1 Thome, C. E., and others. Plans and Summary Tables 
of the Experiments at the Central Farm. Ohio Agr. Exp. Sta., 
Cir. 120, p. 112. 1912. 



612 SOILS: PROPERTIES AND MANAGEMENT 

This balancing effect may be shown in another way. 
Let it be supposed that to 10 pounds of poultry manure 
having a composition of l.() per cent nitrogen, 1.5 per 
cent phosphoric acid, and 0.9 per cent potash, there are 
added 4 pounds of sawdust, 4 pounds of acid phosphate, 
and 2 pounds of kainit. The manure is rendered drier, 
and its composition becomes 0.8 per cent nitrogen, 3.7 
per cent phosphoric acid, and 1.5 per cent potash. It is 
e\ident, from this and the data previously given, that 
the principal benefit of reinforcing manure lies in the 
balancing influence, and that acid phosphate and floats 
are the most desirable to use. 

515. Lime and manure. — Very often it would be a 
saving of labor to apply lime and manure to the soil at 
the same time. This can readily be done with the car- 
bonated forms. Such lime may be mixed with the 
manure, either in the stable or in the pile, without any 
danger of detrimental results. The close union of the 
lime and the organic matter may even increase the solu- 
bility of the former. Caustic compounds of lime, how- 
ever (CaO and Ca(0H)2), must be kept from manure. 
These active forms react with the ammonium carbonate 
coming from the urea, and cause the liberation of the 
ammonia, which may be readily lost in the air : — 

CON2H4 + 2 H2O = (NH4)2C03 
(x\H4)2C03 + Ca(0H)2 = CaCOs + 2 XH4OH 

A stable or a shed containing manure may be at once 
deodorized by the use of quicklime, but only by the loss 
of much nitrogen, which costs on the market eighteen or 
twenty cents a pound. Caustic lime and manure may be 
applied to the same soil by applying the lime ten days 
or two weeks before the manure. The lime will then 



FARM MANURES 613 

have had time to leach into the soil or to largely change 
to a carbonate form. 

516. Composting. — A compost is usually made up of 
alternate layers of manure and some vegetable matter 
that is to be decayed. Layers of sod or of humous soil 
are often introduced. The manure is used to supply 
the decay organisms and to start the action. The foun- 
dation of such a humus manufactory is usually soil, and 
the pile is preferably capped with earth. The compost 
should be kept moist in order to pre\'ent loss of ammonia 
and to encourage vigorous bacterial action. Acid phos- 
phate or raw rock phosphate and a potassium fertilizer 
are often added, to balance up the mixture and make it a 
more effective fertilizer. Lime is also introduced, to react 
with such organic acids as may tend to form and to inter- 
fere with proper decay. Undecayed plant tissue, such as 
sod, leaves, weeds, grass, sticks, or organic refuse of any 
kind, may thus be changed slowly to a humus which will be 
valuable in building up the soil and in nourishing plants. 
Even garbage may be disposed of in such a manner. 

517. Manure and muck. — Muck soil recently re- 
claimed from a swamp condition is usually treated, if 
possible, with a dressing of manure. This is not so much 
for the purpose of adding plant-food as to supply decay 
and decomposition organisms that will break down the 
comjjlicated humic compounds into such forms as may 
be utilized by the crop. Plenty of lime is therefore essen- 
tial in muck, in order to render the effects of this inocu- 
lation effective and lasting. 

518. Effects of manure on the soil. — The direct fer- 
tilizing effect of manure is by no means its greatest 
influence. In the first place, manure as it rots down 
produces humus. This humus increases the absorptive 



614 SOILS: PROPERTIES AND MANAGEMENT 

capacity of the soil. In days it promotes granulation, 
while in sands it acts as a binding agent, lender all con- 
ditions it promotes granulation and tilth. The capacity 
of a soil to resist drought is raised ; its aeration is in- 
creased and drainage is promoted. All these changes 
tend to benefit plant growth and to produce those indirect 
fertilizing effects that are characteristic of farm manure. 

P^rom the chemical standpoint, the presence of manure 
in the soil tends to increase organic acids, notably car- 
bonic acid. The soil minerals are thus rendered more 
easily soluble. The case of the influence of manure on 
the action of raw rock in the soil has already been cited. 
The humus, also, may combine with certain of the mineral 
elements and hold them in a form more easily available 
to crops. Nor is the chemical influence of farm manure 
the final effect. The modification of the soil flora can 
by no means be passed by. Not only are millions of 
organisms added by an application of manure, but those 
already present in the soil are vastly stimulated by this 
fresh acquisition of humic materials. Nitrification, am- 
monification, and nitrogen fixation are all increased to a 
remarkable degree. 

519. Residual effect of manure. — No other fertilizing 
material exerts such a marked residual effect as does 
manure. This is partly because of its indirect physical 
and biological influences, and partly because of the stimu- 
lated root development of the crops grown. The greatest 
residual influence, however, is brought about by the slowly 
decomposable nature of the manure, only a small per- 
centage being recovered in the first crop grown after the 
manure is applied. Hall ^ presents the following data 

1 Hall, A. D. Fertilizers and Manure, p. 210. New York, 
1910. 



FARM MANURES 



615 



from Rothamsted. The crop was mangolds, and the re- 
covery of the constituents carried by the manure was 
very low : — 



Recovery of Nitrogen in a Crop of Mangolds 



Treatment 


Per Acre 


Yield in 
Tons 


Percentage 
Recovery 


Nitrate of soda . . 
Ammonium salts 
Rape cake .... 
Manure 


550 pounds 
400 pounds 
2000 pounds 
14 tons 


17.95 
15.12 
20.95 
17.44 


78.1 
57.3 
70.9 
31.6 



The length of time through which the effects of an 
application of farm manure may be detected in crop 
growth is very great. Hall ^ cites data from the Roth- 
amsted experiments in which the effects of eight yearly 
applications of 14 tons each were apparent forty years 
after the last treatment. This is an extreme case; ordi- 
narily, profitable increases may be obtained from manure 
only from two to five years after the treatment. The fact 
remains, nevertheless, that of all fertilizers farm manure 
is the most la.sting, lends the most stability to the soil, 
and is really a soil builder par excellence. 

520. Place of manure in the rotation. — With a num- 
ber of trucking crops, the application of manure directly 
to the crop year after year has proved to be advisable. 
In an ordinary rotation, however, where less intensive 
methods are employed, it is evident that manure may 
vary in its effect according to the place in the rotation at 



1 HaU, A. D. 
1910. 



Fertilizers and Manure, p. 213. New York. 



616 SOILS: PROPERTIES AND MANAGEMENT 

which it is applied. This has proved to be the case with 
commercial fertilizers, and the fact is also becoming 
recognized in the economic use of farm manures. 

In general, hay has derived more benefit from the re- 
sidual food than almost any other crop in the rotation. 
At the Pennsylvania Experiment Station,' in a rotation of 
corn, wheat, and hay over a test for twenty-five years, in 
which manure was applied in equal amounts to the corn 
and wheat, the results were as follows : — 



Percentage Increase from Use of Manure, and Value of 
THAT Increase 



Treatment 


Corn 


Oats 


Wheat Hay 


6 tons manure 
Cost $9 . . 


37 per cent 
$10.85 


28 per cent 
$3.66 


73 per cent 39 per cent 
$9.70 $6.55 



The same fact has been clearly shown in the Ohio 
experiments - covering a term of eighteen years. The 
query immediately arising here is : If hay responds so 
well to residual feeding, why not apply the manure 
directly to it? On this point the following figures from 
the Illinois Experiment Station ^ may be presented, com- 
paring the response of corn and oats when manured to 
the vield of clover with the same treatment : — 



1 Hunt, T. F. Croneral Fertilizer Experiments. Ann. Rept. 
Pennsylvania Agr. Exp. Sta., 1907-1908, pp. 68-93. 

^ Thome, 0. E., and others. Plans and Summary Tables 
of the Experiments at the Central Farm. Ohio Agr. Exp. Sta., 
Cir. 120, pp. 101-105. 1912. 

^ Hopkins, C (1. Thirty Years of Crop Rotation in Illinois. 
111. Agr. Exp. Sta., Bui. 125, p. 337. 1908. 



FARM MANURES 



G17 





Average Percentage 
Increase 


Total Value op 
Increase 




Corn and 
Oats 


Clover 


Corn and 
Oats 


Clover 


Manure 11 

Manure, lime, and 

phosphate .... 30 


92 
141 


$ 7.53 

12.21 


$10.08 
15.48 



When hay is included in any rotation it is evident that 
the best results from manure may be obtained by placing 
it on this crop. This, however, is often not advisable, 
especially where the amount of manure is limited. A 
commercial fertilizer may take its place on the hay, al- 
lowing the farm manure to be utilized on special crops. 
When applied to hay it should be spread as a light top- 
dressing. When manure is used for such a crop as corn, 
however, it is best plowed under, as the amounts added 
per acre are often large. Farm manure in judicious 
amounts may be harrowed in or plowed under in orchards. 

521. Resume. — From the general discussion already 
presented", it is eviflent that barnyard manure, from the 
standpoint of soil fertility, is the most valuable by-product 
of the farm. A careful farmer will therefore attempt to 
utilize it in the most economical way. The handling of 
manure in such a manner that only a small waste will 
occur from the time when the manure is voided until it 
has reached the land again, is not an easy problem. 
Manure is so susceptible to the loss of valuable ingredients, 
both by leaching and by fermentation, that careful methods 
must be employed. The utilization of tight floors in the 
stable and of covered sheds or manure pits is to be ad- 



618 SOILS: PROPERTIES AND MANAGEMENT 

vised. Hauling immediately to the field is a wise pro- 
cedure. Yet even with, the best of care a loss of from 30 
to 50 per cent is often incurred. A permanent system of 
agriculture evidently cannot be established by simply 
returning all the manure possible to the land. Neverthe- 
less, it is certainly worth the while of any farmer to use 
at least some care in the handling of this product. Even 
reasonable attention would save for the soils of this coun- 
try thousands of dollars' worth of manurial fertility 
which is now carried awa\' in the streams and rivers. 



CHAPTER XXVII 
GREEN MANURES "^ 

From time immemorial the turning-under of a green 
crop to supply organic matter to the soil has been a com- 
mon agricultural practice. Records show that the use of 
beans, vetches, and lupines for such a purpose was well 
understood by the Romans, who probably borrowed the 
practice from nations of still greater antiquity. The art 
was lost to a great extent during the Dark Ages, but was 
revived again as the modern era was approached. At 
the present time green-manuring is considered a part of 
a well-established system of soil management, and is 
given a place, where possible, in every rational plan for 
permanent soil improvement. 

522. Efifects of green-manuring. — The effects of turn- 
ing under green plants are both direct and indirect — 
direct as to the influence on the succeeding crop, and in- 
direct as to the action on the physical condition of the 
soil so treated. In the first place, certain ingredients are 
actually added to the soil by such a procedure. The car- 
bon, oxygen, and' hydrogen of a plant come largely from 

1 Penny, C. L. Cover Crops as Green Manures. Delaware 
AgT. Exp. Sta., Bui. 60. 1903. 

Storer, F. H. Agriculture, pp. 1.37-175. New York. 1910. 

Lipman, J. G. Bacteria in Relation to Country Life, Chapter 
XXIV, pp. 237-263. New York. 1911. 

Piper, C. V. Leguminous Crops for Green Manuring. 
U. S. D. A., Farmers' Bui. No. 278. 1907. 

Spillraan, W. J. Renovation of Worn-out Soils. U. S. D. A., 
Farmers' Bui. No. 24.5. 1906. 

619 



620 SOILS: PROPERTIES AND MANAGEMENT 

the air, and the plowing-under of a crop therefore in- 
creases the store of such constituents in the soil. If the 
plant is a legume and the nodule organisms are active, 
the nitrogen content of the soil is also augmented. The 
mineral parts of the turned-under crop, of course, come 
from the soil originally and they are merely turned back 
to it again. As they return, however, they are in intimate 
union with organic materials, and are thus readily avail- 
able as plant-food as the decay process goes on. Indeed 
they are much more readily a\ailable than they previously 
were, when the green-manuring crop acquired them. 
Actual additions are thus made to the soil, together with 
a promotion of an increased availability of the constit- 
uents dealt with. 

Green manures may function also as cover crops, in 
so far as they take up the extremely soluble plant-food 
and prevent it from being lost in the drainage water. The 
nitrates of the soil are of particular importance in this 
regard, as they are very soluble and are adsorbed only 
slightly by the soil particles. Besides this, green manures, 
especially those with long roots, tend to carry food up 
from the subsoil, and when the crop is turned under 
this material is deposited within the root zone. Again, 
the added organic material acts as a food for bacteria, 
and tends to stimulate biological changes to a marked 
degree. This bacterial action is esj)ecially prone to in- 
crease the production of carbon dioxide, ammonia, ni- 
trates, and organic acids of various kinds, which are very 
important in plant nutrition. The humus that results 
from this decay increases the adsorptive power of the soil, 
and promotes aeration, drainage, and granulation — con- 
ditions that are extremely important in successful crop 
growth. 



GREEN MANURES 621 

523. Quantities of plant constituents added by green- 
manuring. — In an average crop of green manure, from 
five to ten tons of material is turned under. Of this, 
from one to two tons is dry matter, and from four to eight 
tons water. Of this dry matter a great proportion is car- 
bon, hydrogen, and oxygen — a clear gain to the soil in 
so far as these constituents are concerned. The amount 
of nitrogen added to a soil if the green manure is a legume ^ 
is a difficult question to decide. Much depends on the 
virulence of the organisms occupying the nodules. These 
bacteria are in turn much influenced by plant and soil 
conditions. Hopkins ^ estimates that about one-third of 
the nitrogen in a normal inoculated legume comes from 
the soil and two-thirds from the air. He also considers 
that one-third of the nitrogen exists in the roots. It is 
evident, therefore, that in general the nitrogen found in 
the tops will be a rough measure of the nitrogen fixed by 
the soil organisms. If this is returned to the soil, there 
is a clear gain of just that amount. 

If the preceding assumption is correct, clover ^ would 
actually add to every acre about 40 pounds of nitrogen 



1 Smith, C. D., and Robinson, F. W. Influence of Nodules 
on the Roots upon the Composition of Soybean and Cowpea. 
Mich. Agri. Exp. Sta., Bui. 224. 1905. 

Hopkins, C. G. Alfalfa on Illinois Soil. Illinois Agr. Exp. 
Sta., Bui. 76. 1902. 

Hopldns, C. G. Nitrogen Bacteria and Legumes. Illinois 
Agr. Exp. Sta., Bui. 94. 1904. 

Shutt, F. T. The Nitrogen Enrichment of Soils through the 
Growth of Legumes. Canadian Dept. Agr., Rept. Centr. Exp. 
Farms, 1905, pp. 127-132. 

- Hopkins, C. G. Soil Fertility and Permanent Agriculture, 
p. 223. Boston, 1910. 

^ Penny, C. L. The Growth of Crimson Clover. Delaware 
Agr. Exp. Sta., Bui. 67. 1905. 



622 SOILS: PROPERTIES AND MANAGEMENT 

per ton, alfalfa about 50, cowpeas 43, and soy beans 

53 pounds. These figures, even though they may 
be far from correct, at least give some idea as to the 
possible addition of nitrogen by green-manuring prac- 
tices, and show how the soil may be enriched by such 
management. As in the case of farm manures, the in- 
direct effects of such a procedure may override the 
direct influences, making the use of legumes as green- 
manuring crop less necessary than at first thought might 
be supposed. 

524. Decay of green manure. — As a green crop enters 
the soil, the process of its decay is the same as that of 
any plant tissue that becomes a part of the soil body. 
The organisms that are active are those common to the 
soil, together with such bacteria as are carried into the 
soil on the turned-under crop. The decay should be 
accomplished under aerobic conditions so that only 
beneficial products may result. Plenty of water is a 
necessity, as otherwise the soil would be robbed of a 
part of its available moisture in facilitating the process of 
decay. When proper decay has occurred, end products 
should result which can be utilized as plant-food. The 
intermediate compounds that are formed should yield a 
black humus, should readily split up into simple com- 
pounds, and should be in general beneficial, both directly 
and indirectly, to crop growth. The decay of green 
manure under conditions of poor drainage and improper 
aeration is likely to cause the generation of materials 
detrimental to the proper development of plants. 

525. Crops suitable for green manures. — The crops 
that may be utilized as green manures are usually grouped 
under two heads, legumes and non-legumes. Some of the 
common green manures are as follows : — 



GREEN MANURES 



623 





Legumes 


Non-legumes 


Annual 




Biennial 




Cowpea 




Red clover 


Rye 


Soy bean 




White clover 


Oats 


Peanut 




Alsike clover 


Mustard 


Vetch 




Alfalfa 


Mangels 


Canada field 


pea 


Sweet clover 


Rape 


Velvet bean 






Buckwheat 


Crimson clover 






Hairy vetch 









When other conditions are equal, it is of course always 
better to choose a leguminous green manure in preference 
to a non-leguminous one, because of the nitrogen that may 
be added to the soil. However, it is so often difficult to 
obtain a catch of some of the legumes that it is poor 
management to turn the stand under until after a number 
of years. Again, the seed of many legumes is very expen- 
sive, almost prohibiting their use as green manures. 
Among the legumes most commonly grown as green ma- 
nures, cowpeas, soy beans, and peanuts may be named. 
Many of the other legumes do not so fit into the common 
rotations as to be handily turned under as a green manure. 

For the reasons already cited, the non-legumes have in 
many cases proved the more popular and economic as 
green manures. Rye and oats are much used because 
of their rapid, abundant, and succulent growth and be- 
cause they may be accommodated to almost any rotation. 
They are hardy and will start on almost any kind of a 
seed bed. They are thus extremely valuable on poor soils. 
Often the value of such a green manure as oats is greatly 
increased by sowing peas with it. The advantages of a 
legume and a non-legume are thus combined. 



624 SOILS: PROPERTIES AND MANAGEMENT 

526. When to use green manures. — The indiscrimi- 
nate use of green manures is of course never to be ad- 
vised, as the soil may be injured thereby and the normal 
rotation much interfered with. When soils are poor in 
nitrogen and humus, they are very often in poor tilth. 
This is true whether the texture of the soil be fine or 
coarse. The turning-under of green crops must be judi- 
cious, however, in order that the soil may not be clogged 
with undecayed matter. Once or twice in a rotation is 
usually often enough for such treatments. Proper drain- 
age must always be provided. In regions where the rain- 
fall is scanty, very great caution must be observed in the 
handling of green manures. The available moisture that 
should go to the succeeding crop may be used in the 
process of decay, and the soil left light and open, due to an 
excess of undecomposed plant tissue. 

527. When to turn imder green crops. — It is generally 
best to turn under green crops when their succulence is 
near the maximum. In this case a large cjuantity of water 
is carried into the soil, and the draft on the original soil 
moisture is less. Again, the succulence encourages a 
rapid and more or less complete decay, with the maximum 
production of humus and end products. The plowing 
should be done, if possible, at a season when a plentiful 
supply of rain occurs. The effectiveness of the maiuiring 
is thereby much enhanced. 

528. How to turn imder green material. — In general, 
in turning under green manures the furrow slice should 
not be thrown over flat, since the green crop is then de- 
posited as a continuous layer between the surface soil 
and the subsoil. Capillary mo\ement is thus impeded 
until a more or less complete decay has occurred, and the 
succeeding crop may sufTer from lack of moisture. 



GREEN MANURES 625 

The furrow ordinarily should be turned only partly 
over, and thrown against and on its neighbor. The green 
manure is then distributed evenly from the surface down- 
ward to the bottom of the furrow. When decomposition 
occurs the humic materials are evenly mixed with the 
whole furrow slice. Moreover, this method of plowing 
does not interfere with the capillary mo^•ements of water, 
and in actual practice is a great aid in drainage and 
aeration. 

529. Green manures and lime. — The decay of organic 
matter in the soil is always accompanied by the produc- 
tion of organic acids. Such acids tend to form in large 
amount, especially if the fermenting matter is of a suc- 
culent nature. The need of plenty of lime under such 
conditions is clearly apparent, as a soil of a neutral or an 
acid character may assume a bad condition during the 
process of humic decay. Lime may be added to the green- 
manure seeding and be turned under with that crop. 
The amendment would thus be in very close contact with 
the decaying vegetable tissue. Ordinarily, however, the 
application of lime at some point in the rotation is suffi- 
cient. 

530. Green manure and the rotation. — Very often it 
is somewhat of a problem as to when, in an ordinary rota- 
tion, a green manure may be introduced so that it may 
fit in well with the crops grown. In a rotation of corn, 
oats, wheat, and two years of hay, a green manure might 
be introduced after the corn. This would not be a very 
good practice, however, as a cultivated crop should 
usually follow a green manure so as to facilitate decom- 
position and decay. In such a rotation the plowing- 
under of the hay stubble is really a form of green-manur- 
ing, there being a considerable accumulation of roots, 

2s 



626 SOILS: PROPERTIES AND MANAGEMENT 

stubble, and aftermath on the soil. When a rotation of 
this kind is used it is better either to supply organic 
matter in other ways, or to alter or break the rotation in 
such a manner as to admit of a more advantageous use 
of green crops. 

Where trucking crops are grown and no \ery definite 
rotation is adhered to, green-manuring is easier. It is 
especially facilitated when cover crops are grown, as in 
orchards. Soiling operations also favor the easy and 
profitable use of green manures. In general it may be 
said that the organic matter obtained from such a source 
should be supplemented by farmyard manures where 
possible. A better balanced and richer soil humus is 
more likely to result. 



CHAPTER XXVIII 
LAND DRAINAGE 

Land drainage ^ is the process of withdrawing from the 
soil the superfluous or gravitational water occurring in 
the larger spaces within the normal root zone. Excess 
moisture in the soil interferes with ventilation, keeps 
down the temperature, and seriously disturbs the physical 
nature of the soil. Any means that permits the free flow 
from the soil of the gravitational water afl^ords drainage. 
Many methods are used, according to circumstances. 
Indications of the need of drainage are the presence of 
free water in the surface soil and in excavations into the 

1 Elliott, C. G. Engineering for Land Drainage. New 
York. 1912. 

Fanre, L. Drainage et Assainissement Agricole des Terres. 
Paris. 1903. 

King, F. H. Irrigation and Drainage, Part II. New York. 
(Revised edition. 1909.) 

Klippart, J. H. Principles and Practice of Land Drainage. 
Cincinnati. 1894. 

Woodward, S. M. Land Drainage by Means of Pumps. 
U. S. D. A., Office Exp. Sta., Bui. No. 243. 1911. 

Warren, G. M. Tidal Alarshes and their Reclamation. 
U. S. D. A., Office Exp. Sta., Bui. No. 240. 1911. 

Elliott, C. G. Drainage of Farm Lands. U. S. D. A., 
Farmers' Bui. No. 187. 1904. 

Miles, M. Land Drainage. New York. 1897. 

See also the following bulletins of state experiment stations : 
Michigan, Sp. 56; Maryland, 186; New York (Cornell), 254; 
Utah, 123; Wisconsin, 138, 199, 229; Ontario, Canada, 174, 
175. 

627 



628 SOILS: PROPERTIES AND MANAGEMENT 

subsoil ; and the tendency of the soil to puddle and bake 
when dry. When the wetness is prolonged, the accu- 
mulation of organic matter in the surface soil imparts a 
dark color. Poor drainage causes a mottled color in the 
subsoil, and in extreme cases a pale gray color resulting 
from excessive leaching. When the land is in crops the 
wet places are recognized by their miry condition in early 
spring and after rains, and by the slow starting of the 
crop. In meadows the grass is often winterkilled, leaving 
only those weeds that can withstand the conditions. 
Heaving of soil is another indication of wetness. In tilled 
crops the wet spots are often marked by the small growth 
of the plants and by curled, wilted leaves in dry periods. 
In orchards weakened and missing trees are in many 
cases an indication of defective drainage, especially in the 
subsoil, where the roots of older trees seek to develop. 

Steeply sloping hill land may need drainage quite as 
much as flat land if it has a compact subsoil overlaid by a 
porous topsoil. Water is then trapped in the soil, and is 
removed very slowly by percolation on top of the hard 
subsoil and by evaporation. It is wet land in need of 
drainage. 

531. Extent of drainage needed in humid regions. — 
The amount of farm land in need of some drainage is very 
large. Besides the land commonly designated as swamp 
and marsh, there are very large areas of land devoted to 
crop production, the yields from which are reduced by the 
excess of water that they contain at certain seasons of the 
year. The extent of swamp land varies in different coun- 
tries, but is likely to aggregate about five per cent of the 
total area. The croi)ped land in need of some drainage is 
very much larger, and roughly aggregates three-fourths of 
the total improved land surface. The temporary wetness 



LAND DRAINAGE 629 

that much land experiences is often more injurious than 
the prolonged wetness of swamp land. On the latter 
there is no loss except on the investment value of the land, 
which is likely to be low. On the tilled land, however, a 
considerable sum of money is expended for labor, seed, 
and perhaps fertilizers and manures, without corresponding 
returns. The loss under these conditions may be heavy. 
For the ordinary farm and garden crops, the fluctuation 
of the soil moisture from a condition of somewhat pro- 
longed saturation to the dry and often hard condition 
that usually results is exceedingly difficult to withstand. 
Drainage is concerned not only with the surface and the 
topsoil water, but also with the subsoil- water to the depth 
to which the roots of crops normally penetrate. 

532. History of drainage. — The need for soil drainage 
in the production of the ordinary farm and garden crops 
on many soils has been recognized from the beginning of 
historic times. The old Roman husbandman Cato,^ and 
his successors of the next ten centuries, in their writings 
on agriculture pointed out the importance of draining wet 
soil, and Cato explains how bundles of faggots should be 
buried in trenches in the land. In western Europe ^ 
artificial drainage has been practiced for some hundreds 
of years. In England within the last two hundred years 
drainage by means of pipes has become a general practice. 

The practice of underdrainage by means of clay tile 
was begun in America in the early part of the nineteenth 

' Cato, M. P. Roman Farm Management by a Virginia 
Gentleman. New York. 1913. 

2 Elliott, C. G. Engineering for Land Drainage. New 
York. 1912. 

Miles, M. Land Drainage, Chapter VI. New York. 1892. 

French, H. F. Farm Drainage, Chapter IL New York. 
1859. 



630 SOILS: PROPERTIES AND MANAGEMENT 

century. John Johnston,' a Scotchman Uving near 
Geneva, New York, carried out the most extensive of 
these pioneer enterprises, beginning about ISIio. A very 
thorough system of tile drains, aggregating about sixty 
miles in length, was installed on his farm of three hundred 
acres, and these drains are still in operation and are pro- 
ducing excellent results. 

533. Effects of land drainage on the soil. — The need 
and value of thorough drainage of the soil can often be 
better appreciated after a careful summary of its efl'ects 
on the properties that determine crop growth. From a 
study of these it may be seen that for the production of 
the ordinary upland crops a reasonable amount of soil 
drainage is the first requisite. It may well be termed 
the foundation of good soil management. The more 
noticeable effects are as follows : — 

1. Drainage permits the development of the granular 
structure in soils, especially in those containing much 
clay, and thereby permits the creation of a much better 
tilth. This tilth is brought about by the frequent changes 
in moisture content of the soil made possible by drainage, 
coupled with other natural and artificial agencies, as has 
already been explained. As a result the soil maintains 
the open and friable condition favorable for the absorp- 
tion of rain water, and the circulation of the water in 
the spaces in the soil without interference with the crop 
roots. The tendency of the soil to puddle and form 
large, hard lumps is rerluced. 

2. The withdrawal of the excess water from the larger 
spaces in the soil permits the admission of air into those 

1 Mellen, C. R. History and Results of Drainage on the 
John Johnston Farm. Proc. New York State Drainage Assoc, 
pp. 27-32. 1912-1913. 



LAND DRAINAGE 631 

spaces. This results in better ventilation. The free 
movement downward through the soil of the waves of 
saturation accelerates the process of deep soil ventilation 
by driving the contaminated air out through the under- 
drains while fresh air is drawn in behind the wave of soil 
moisture. 

3. The removal of the excess moisture by drainage 
permits the soil to maintain a higher average tempera- 
ture. The high specific heat of water as compared with 
the soil causes the presence of water to be the chief deter- 
mining factor in soil temperature. Further, the process 
of evaporation of the excess water from the soil requires 
a tremendous amount of heat. The use of solar heat to 
warm useless water and to remove it by evaporation is 
avoided by draining away this excess. Drained soil not 
only maintains a higher average temperature in summer, 
but warms up earlier in spring to a temperature for 
planting seeds. This gives a longer growing season. 

4. The improved ventilation resulting from drainage 
permits the roots of plants to penetrate deeper into the 
soil, where they come in contact with a larger supply of 
moisture and food. One of the indications of the need of 
drainage is the shallow root development of crops. Stag- 
nant water in a saturated soil is as resistant to the pene- 
tration of upland crops as is the hardest rock ( see Fig. 
63). 

5. The improved phj^sical condition of the soil that 
results from drainage permits the retention of a larger 
amount of film water, and this, in time of drought, re- 
sults in a much larger available supply of moisture to 
the crops. 

6. The improved pliysical condition of the soil permits 
better internal circulation of water, by which the films are 



632 SOILS: PROPERTIES AND MANAGEMENT 



renewed and the excess water is permitted to pass away 
quickly in the drainage channels. 



fc-> p-^-- , jv -ji 



W 









Fig. 63. — Area of land nearly level, but having compact subsoil wnth 
undulating subsurface, thereby causing wet pockets that force 
plants to form short roots. Weeds are abundant in such areas. 
Drainage removes the water and permits deeper penetration of the 
plant roots, thus enlarging their feeding zone. 

7. The improved ventilation and higher temperature 
due to drainage promote the activity of decay organisms, 
by which fresh organic matter is changed into forms that 
may be used as food by crops. This aids in the formation 
of humus, with its beneficial physical effects on the soil. 

8. The higher temperature, better ventilation, better 
distribution of moisture and of decayed organic matter, 
together with the deeper penetration of roots, make avail- 
able a larger amount of mineral elements from the soil 
particles. 

9. It may now be recognized that there is a distinct 
sanitary aspect to soil management. The accumulation 
of materials of a toxic nature is promoted by poor drain- 
age, and their destruction is hastened, and perhaps in 
part their formation is prevented, by the conditions 
that accompany good soil drainage. 

10. Drainage reduces heaving. Heaving, or "the lifting 
of crops by frost action in the soil, indicates the presence 



LAND DRAINAGE 633 

of too much moisture iu the soil in proportion to its 
pore space. When water freezes it expands one-eleventh 
of its volume. If the soil is too nearly saturated, this ex- 
pansion is expressed at the surface of the soil by a lifting, 
or heaving, which is exceedingly injurious to most crops 
that pass the winter in the soil. It breaks their roots 
and gradually lifts the smaller plants out of the ground 
if the process is many times repeated. When the soil is 
drained so that free air spaces are distributed through 
the mass, the expansion of the w^ater as it freezes is taken 
up in these spaces without heaving at the surface. 

11. Drainage reduces erosion of soils by withdrawing 
the water through the soil instead of permitting it to 
accumulate to the point where it must move over the 
surface, often with serious erosive action. In order that 
the drains may be efficient, the soil above the drains must 
be sufficiently porous to permit the removal of the water 
as fast as it accumulates. 

12. Thorough soil drainage greatly increases the effi- 
ciency of all equipment and practices used in crop produc- 
tion on the farm. There is a longer time in which to do 
the work, a longer season in which the crop may grow, 
and usually less labor is required in order to fit the land 
and keep it properly tilled. Further, the crop matures 
more evenly and is likely to be of better quality. The 
need for a commercial fertilizer is reduced because of the 
higher efficiency of the soil. 

13. Prompt and thorough drainage of a wet soil results 
in a large increase in yield and quality of crops. All the 
common farm, garden, and orchard crops are injured by 
a saturated condition of the soil, and the changes that 
accompany the correction of that condition permits a 
large growth of the plants. The fundamental nature of 



634 SOILS: PROPERTIES AND MANAGEMENT 

those changes, and therefore the basic importance of good 
drainage of the soil, is indicated l)y this summary of 
effects. Even where ordinary yields of crops can be 
grown, improved drainage will usually increase the yield 
10 per cent or more ; and increases of several hundred 
per cent are in many cases realized where the conditions 
before drainage were particularly bad. Land in need of 
drainage is in many cases fertile in all other respects, and 
when the soil moisture is properly adjusted it responds 
with large yields. Proper drainage should be the starting 
point in any permanent improvement of the soil. 

534. Methods of drainage. — Two general methods of 
drainage are employed: (1) open ditches, and (2) closed 
drains, or underdrains. 

Open ditches are most satisfactory where the N'olume 
of water to be moved is very large. The general drainage 
of a region is usually carried in open ditches. ■ They are 
used where the land is exceedingly flat, and especially if 
the land level is very near the level of the water in the 
outlet channel so that only a small head can be developed. 
They are used also where a temporary result is desired. 

There are many objections to open ditches, either large 
or small, especially as applied to tilled land. They waste 
a considerable area of land in the channel and on the 
banks, and they interfere with free tillage operations. In 
the case of small field ditclies this interference is serious. 
The ditch bank promotes the growth of weeds. The 
shallow surface trenches conunonly used to remove stand- 
ing water from the land are of very low efficiency, since 
they do not remove the water from the subsoil and often 
are so shallow that the surface soil remains almost satu- 
rated. Water flows slowly in such rough, irregular 
channels. 



LAND DRAINAGE 635 

The cost of maintenance of a system of open ditches is 
heavy, because of erosion, the accumulation of sih, and 
the growth of weeds, all of which make frequent repairs 
necessary. 

Underdrains when properly constructed are more 
permanent than open ditches and cost less for mainte- 
nance. They do not interfere with surface operations. 
The better grade gives them a relatively larger carrying 
capacity than open ditches have, and their greater depth 
below the surface permits much higher efficiency in the 
removal of excess moisture from the root zone. 

535. Construction of small open ditches. — Small 
field ditches may be used in the field to remove small 
accumulations of surface water. They usually consist of 
a furrow run in the lowest parts and made with a large 
single shovel plow, with a turning plow, or with a two- 
way plow having moldboards to turn the soil on either 
side. Another modification in the construction of open 
ditches, which is frequently combined with the foregoing, 
is the use of " dead furrows." The land is plowed in 
narrow beds two or three rods in width, with a deep 
" dead " furrow between each which drains off some of 
the surplus water from the higher parts of the intervening 
area. A further modification is sometimes used in plant- 
ing cultivated spring crops on wet land. Ridges are 
thrown up along each row and the seed is planted on these 
ridges. The intervening trench affords some drainage. 

536. Construction of large open ditches. — Where 
larger \olumes of water must be removed, a larger channel 
is necessary, its size being determined by the area to be 
drained, the grade of the ditch, its length, its straightness, 
and the smoothness of the sides and bottom. The ideal 
shape for the ditch for the largest carrying capacity is a 



68G SOILS: PROPERTIES AND MANAGEMENT 

semicircle. In this form the ditch is one-half as deep as 
it is wide at the surface. This brings the minimum sur- 
face in contact with the moving water. The tendency 
of the banks to cave near the top, as well as the diffi- 
culty of constructing such a form, has led to the modifi- 
cation of the walls to an inclined slope that is normally 
one to one, or an angle of forty-five degrees. This angle 
is further modified by the nature of the soil through which 
the ditch passes, and is steeper in clay soil and less 
steep in loose sandy soil. Where the land is very flat 
and near the level of the water in the outlet channel, it 
may be desirable to deepen the ditch considerably below 
the minimum level of water in order to increase the flow 
during freshets. 

The shape may be further modified where the volume 
of water to be carried varies excessively. A wide channel 
may be provided to accommodate the flood water, and 
in the bottom of this channel a smaller channel may be 
provided for the normal flow, of such a size that it is more 
likely to be kept clean and free than would a ditch of 
larger cross section in which the water would be shallow. 

An open ditch should be kept as straight as possible so 
as to avoid erosion of the banks where turns occur. Change 
of direction should begin gradually and should have the 
maximum curvature at the middle of the turn. It should 
then pass gradually on into the straight line of the new 
direction. 

The grade will naturally conform in a large measure to 
the surface of the ground, but it may need to be modified 
from the natural grade where the slope is so steep as to 
cause serious erosion. This difficulty receives special 
attention in constructing canals to carry irrigation water. 
Sandy soils having low cohesion are most subject to 



LAND DRAINAGE 637 

erosion on hi<ib j^rades. Fine-textured clays are least 
affected by erosion. The grades and rates of flow that 
are permissible depend largely on the size of the ditch. 
A velocity of three feet a second is usually the maximum 
that is permissible. It may be a little higher in clay, 
and should be a third lower in silt and fine sandy loam. 
This rate of flow may be attained in ditches where the 
water is several feet deep by a fall of only six inches to a 
foot a mile. In small ditches where the water is a foot 
or less in depth the grade may be from fifty to sixty feet 
a mile, and in heavy clay, especially if it is compact and 
stony, a still higher grade will not cause serious washing. 

These limits depend to a large extent on the amounts 
of sediment that the water carries. Material in suspen- 
sion greatly increases erosive action on the ditch walls. 

In constructing open ditches care should be taken to 
deposit the earth several feet back from the edge of the 
channel. This is desirable for two reasons : first, it re- 
moves the weight from the unsupported bank, where 
caving is very likely to occur when the soil is saturated ; 
second, it provides a larger throat for the stream should 
it be inclined to overflow. 

Another method of constructing an open ditch, es- 
pecially in wet grass land, is to form a broad, shallow 
chainiel by the use of a road scraf)er. The earth is 
gradually worked back a rod or more, and the walls are 
so flat, even with a ditch three feet deep, that crops grow 
and may be collected in the bottom of the ditch. This 
system reduces the loss of land and the interference with 
farm operations. 

537. Construction of early types of underdrains. — 
Any material or condition that affords an underground 
passage for the flow of water measurably fulfills the func- 



638 SOILS: PROPERTIES AND MANAGEMENT 

tion of an iinderdrain. Many methods and materials 
have been employed. One used in England in clay soil 
is termed mole drainage. A plow having a long, thin 
shank, with a molelike or cigar-shaped point at the 
bottom, is slowly drawn through the soil by teams or a 
capstan. The passage formed persists for several years 
in the finer and more coherent classes of soil, and may 
do good service. Soil free from stones and having a con- 
siderable degree of plasticity is necessary for this method 
to have much value. 

In ancient times, and in pioneer days in America, 
bunches of faggots, brush, poles, rails, straw, and wooden 
boxes of triangular or square shape, have been extensively 
employed for underdrainage and have been very useful. 
They may still have some use, but they have generally 
been superseded by more permanent, if not more efficient, 
materials. 

538. Stone drains. — Wherever stones are abundant 
they have been placed in trenches in some manner and 
often have served for many years to facilitate the removal 
of excess Avater from the soil. Wliere there are flat stones 
they may be arranged to form a continuous throat. 
Several systems of arrangement have been used. All 
throated drains are more likely to be closed by sediment 
than a drain with no single, distinct throat. Perhaps 
the safest arrangement is to place flat stones on edge in 
the trench, with their faces parallel to one another and 
to the Avails of the ditch, depending on the irregularities 
between their faces for the flow of the water. Flat stones 
are placed over the top of the vertical stones. Where 
round stones are available the safest method is to place 
them in the trench without any arrangement except to 
put the small stones on the surface. The water will find 



LAND DRAINAGE 



639 



its way through the openings. All stone drains are 
Ukely to be of short (hiration because of obstructions that 
(levek)p in the channel by the accumulation of sediment, 
often promoted by the burrowing of animals. The 
throat of a ditch, to receive stone or brush, should be 
relatively large (see Fig. 64). 





Fig. 64. — The most common types of drainage tile and other materials 
used for land drainage. (1), cobblestones with smaller pieces of 
stone on top ; (2) , flat stones placed face to face and parallel to line 
of ditch ; (3) and (4) , throated drains constructed of flat stones 
used in different ways ; (5), pole drain; (6), triangular box drain; 
(7): square box drain. Note construction for admission of water 
along lower edge ; (8) , horseshoe tile laid on a board ; (9) , horse- 
shoe tile, bottom attached; (lO), single sole tile with round open- 
ing; (11), double sole tile; (12), hexagonal tile; (13), round tile; 
(14), Y-shaped junction piece; (15), elbow piece. 



539. Tile drains. — Modern underdrainage is usually 
accomplished by means of short sections of pipe of burned 
clay or concrete, placed in the ground sufficiently deep to 
lower the water table in the subsoil to the desired depth 
within two or three days. They are given an accurate 
grade, and this, coupled with the smooth, hard channel 
which is not "subject to erosion, makes them a very effi- 



640 ROILS: PROPERTIES AND MANAGEMENT 

cient as well as a \'ery permanent means of land drainage 
at relatively small cost. If they are well installed and of 
good material, they should continue to operate for cen- 
turies with very little attention. As noted above, tile 
drains have been in continuous operation in America for 
s?venty-five years and are still firm and efficient. 

540. Quality of tile. — There ma\' be a considerable 
range in the quality of tile made of either clay or concrete. 
Clay tile is made of several grades of clay and sand mixed 
and burned at a high temperature. Material that is 
fused slightly is thereby vitrified, and forms a tile having 
a very dense, impervious wall. This is vitrified tile. 
Burned at a lower temperature the walls are more porous 
and less resistant. Some material does not fuse at any 
temperature to which it may be raised, and produces a 
tile having soft, porous walls. This makes soft, or brick, 
tile. Still another grade of tile is made of clay — usually 
fire clay — dipped into a salt solution before firing. This 
gives a smooth glaze, commonly seen in sewer tile. This 
is glazed tile. 

Of the three grades mentioned, the vitrified tile is 
normally the best because of its strength and resistance 
to the destructive agencies in the soil. The most notice- 
able of these agencies is frost. Even burned clay cannot 
resist the destructive action of freezing water. Any tile 
that has walls porous enough to absorb an appreciable 
amount of water — and the larger the amount, the greater 
is the danger — will, if frozen and thawed a few times, be 
shattered into flakes. The walls of soft tile will absorb 
capillarily from 8 to 20 per cent of moisture, and under 
the action of frost will go to pieces rapidly. Glazed tile 
is less injured, especially when the glaze is intact ; but 
once a crack has formed the tile is rapidly destroyed. 



LAND DRAINAGE 641 

The vitrified tiles have walls so dense that they absorb 
less than 3 or 4 per cent of moisture, and often less than 
2 per cent, so that they are much less vulnerable to frost 
action. Good tile should be well formed and should 
give a clear ring when struck with a hammer. 

Concrete tile of good quality may be made, but the 
quality is normally inferior to that of the best vitrified 
tile. The porosity is likely to be 5 to 10 per cent. To 
make good cement tile requires a rich proportion of cement, 
good sand, and as w^et a mixing and molding as is prac- 
ticable. Several machines of both farm and factory size 
are in the market for molding concrete tile. 

Water enters tile through the joints, not through the 
walls. Even the most porous tiles having a high absorp- 
tion do not permit an appreciable amount of water to 
pass through the walls. Therefore, soft tiles have no 
higher efficiency than vitrified tiles, and, owing to the 
risk of freezing, the effectiveness of a line of porous tiles 
is much jeopardized. Since water enters at the joints of 
the tile, short lengths are more efficient than long lengths. 
The usual length of sections of tile under 12 inches in 
diameter is 12 to 13 inches. In larger sizes, where the 
carrying function predominates over the collecting func- 
tion, lengths of 2 feet are employed. 

541. Shapes of tile. - — Tile should have a round open- 
ing and a round or a hexagonal exterior. A flat-bottomed 
opening is objectionable because it reduces the flow and 
promotes the accumulation of sediment. U-shaped tiles 
with flat sides are called horseshoe, or single-sole tile. 
This shape is unsatisfactory. Tiles are often w^arped 
in the process of drying and burning, and the last-named 
shape does not allow a close joint to be formed by turn- 
ing the tile. Round and hexagonal shapes permit turn- 
2t 



642 SOILS: PROPERTIES AND MANAGEMENT 

ing until a good joint is formed. An earlier type was 
the U-shaped tile laid on a board. These tiles are easily 
broken by the pressure of the earth. They are no more 
efficient than the ordinary round tile. 

542. Protection of joints. — Soil water should enter 
the tile at the lower side of the joint. Any unusual 
opening in the joint should be on the lower side. If the 
soil has low coherence, such as may be the case with fine 
sand and silt, the upper half of the joint should be pro- 
tected against the entrance of sediment. A cap of paper 
or of burlap cloth, two or three inches wide and long enough 
to cover the upper half of the joint, may be used. 

Other methods of protecting joints are to co^•er them 
with clay, thick cement mortar, or the sod and granular 
soil from the surface. The last named is most commonly 
employed. Filters may be constructed by placing around 
the tile a layer of coarse sand or gravel, cinders, straw, 
or leaves. Where the soil is of a serious quicksand nature 
(clean, fine sand or silt filled with water), it may be desir- 
able to place a bed of gravel or cinders under the tiles 
as well as around them. The entrance of water from the 
lower side of the joint in small trickles will generally 
prevent any difficulty from sediment. Water should 
flow from a drain approximately clear, and any other 
condition usually indicates a too rapid entrance of water. 
Where the soil is a fine clay with high cohesion, the ends 
of tiles should not be so close together as in loose soil. 
The tops may sometimes be separated an eighth of an 
inch with entire safety. In such cases it is especially im- 
portant to return the soil to the trench in a dry condition 
and to place the t()i)s()il next to the tile. 

543. Entrance of roots into tile. — The entrance of 
roots into the joints of tile drain sometimes causes an 



LANB DRAINAGE 643 

obstruction by breaking up into such a mass of fine root- 
lets that the tile is finally closed. Any kind of tree or 
plant may cause this difficulty if permitted to develop 
under certain conditions. Trouble from roots occurs only 
where the tile carries water from a spring or some other 
continuous source, so that in dry periods the water may 
leak out at the joints into the adjacent dry soil. This 
leads the roots in the. direction of the tile. In the ab- 
sence of such a spring, plant roots do not appear to inter- 
fere with drains. Where a drain carrying water con- 
tinuously comes near a tree, especially if the adjacent 
soil is likely to become dry, the joints of tile should be 
closed by cement. 

544. Protections of joints on curves. — Special care 
may be needed in order to protect the joints on turns 
where the outer side may be too open. The larger the 
size of the tile, the longer will be the opening on a given 
curve. Short turns should not be made. Stones are 
usually unsafe material to place around the joints of a 
tile under such conditions, especially in ^oil that is likely 
to erode easily. If so used, special care should be em- 
ployed to protect the joints with caps. 

545. Foundation for tile. — Tiles should have a firm 
foundation, and if the bottom of the ditch is soft it may 
be advisable to bed them in sand or cinders or lay them 
on a board. Soft muck and quicksand make this most 
necessary. Ordinarily the bottom of the trench is finished 
on the undisturbed earth, which affords a firm setting. 

546. Arrangement of drainage systems. — The ar- 
rangement of a system of underdrains should be deter- 
mined by the slope of the land and the structure of the 
soil. No fixed rule can be laid down. The aim must be 
to place the drains in the line of movement of water in 



644 SOILS: PROPERTIES AND MANAGEMENT 

the soil, and thereby intercept its flow. The need of 
drainage may arise from several conditions. It is always 
indicated by the occurrence of a stratum of rather com- 
pact soil which intercepts the natural flow of water and 
brings it within the root zone. Sometimes this obstruc- 
tion is near the surface, sometimes it is several feet below 
the surface. The water may be brought to the surface 
in a single spring or in a series of springs, in the latter 
case forming a seepage line. The retaining layer may 
have an uneven surface and form basins and hollows 
disguised by a covering of porous soil. For all these 
reasons, the drainage conditions of the soil and the lines 
of movement of water through it should be studied as 
fully as possible before the drainage system is planned. 
The main lines should first be located. Where the land 
is in need of drainage in parts, a few lines of tile will 
accomplish this. Springy holes should generally be ta])ped 
by the most direct route. Often, short wing drains may 
be necessary at the upper end, to collect the underground 
flow. (See Fig. 65.) 

Where there is a line of seepage at nearly a uniform 
level, a drain placed across the slope at the upper edge 
of the wet area, and if possible cutting to the imderlying 
hard stratum, will intercept the flow and meet the needs of 
the lower land. This is an intercepting system of drains. 

Where the land is more nearly uniform in its need of 
drainage, a regular system is required and will usually 
result in a saving of tile. This arrangt^ment should 
approximate a rectangular system, in order to a\'oid 
double drainage where lateral tile join the main line. 
This may of course be modified according to conditions. 
The line of tile should be as long as is practicable for 
convenience in construction. To this end, if the field 



LAND DRAINAGE 645 

is wide in proportion to the length of the main drains, 
the subdrains may branch out hiterally at a right angle 
or less. If the laterals on either side of the main drain 
join at the same acute angle, the " herring-bone " system 




Fig. 65. — Seotioiiil view of soil and rock formation showing the under- 
ground movement of water and the position of resulting wet areas 
on the surface. In addition to the springy places, the soil is kept 
wet by the seepage of water along the top of the compact subsoil. 
This figure also illustrates the reason for locating a cross drain 
above the springy area in order to effect drainage. This method 
cuts off the water supply. 

is formed. If the main drain is situated in the wettest 
part of the field, this system has .some advantage. If the 
field is long and very narrow, the main drain may be along 
the short side of the field, with long laterals leading up the 
slope. If the land is of about equal wetness on a slope, 
the drains should extend up and down rather than across 
the slope. 

547. Grade of tile drains. — ^Yhere the land is rela- 
tively flat or uneven, a survey should be made in order 
to determine the distribution and extent of the grades. 
This is necessary in arranging the system. Where the 
grades are simple, the arrangement may be determined 
by the eye, if the man in charge is experienced. 



646 soils: properties and management 

Tile drains operate best on a j^rade of one or two feet 
in a hundred. Larf:;er grades arc permissible, but in 
such cases the earth should be carefully packed around the 
tile in filling. Tile will operate even on the very slight 
grade of one or two inches in a hundred. In this case 
the minimum size of tile should be larger than on high 
grades, and the distribution of the fall should be very 
uniform. Every part of the operation of planning and 
construction should be guided by readings of an accurate 
level. 

548. Depth of drains. — The depth of tile drains should 
ordinarily be from two feet to three and one half feet. 
The former depth should be the one for clay loam 
or other moderately impervious soil, and is adequate 
for most crops having a shallow root penetration. The 
greater depth should be used on sandy and gravelly soil 
and where deep-rooted perennials are to be grown. Under 
special conditions the drains may be laid deeper or less 
deep than these figures. On \'ery dense clay or where a 
very imperA'ious hardpan exists, the drains may be placed 
a little nearer the surface, since their function is primarily 
to remove the water trapped near the surface. To 
intercept deep underground flow or to secure an outlet 
for it, or where especially deep rooting of crops is desired, 
drains may be laid deeper than the normal. 

Where the soil is sufficiently porous to permit reasonably 
free percolation of water, as in gravelly and sandy sub- 
soils, the deeper drains operate earlier after a rain and are 
the more efficient. The immber of drains necessary is 
also reduced by laying them deci)cr. Where the subsoil 
is relatively impervious, shallow drains should be in- 
stalled and placed as near the top of the impervious layer 
as is practicable. A shallow trench should be formed in 



LAND DRAINAGE 



647 



the compact layer to receive the tile, and if its depth 
exceeds half the diameter of the tile special care should 
be taken to place the topsoil or some other porous material 
on the tile and around the joints in order to insure the 
entrance of water. 

549. Distance between drains. — The interval be- 
tween drains must be determined by the nature and the 
w^etness of the soil and the value of the crops produced. 
In soil where drains must be installed at a depth of two 
and a half feet or less, for general farming the interval 
between drains must ordinarily be not more than fifty 
feet. Where they may be placed deeper, the interval 
may be correspondingly greater. 

The number of feet and rods of tile required when the 
lines are laid regularly at a specified distance apart is 
given in the following table : — 



Distance Apart in Feet 


Tile to the Acre 








Feet 


Rods 


20 


2,178 


131.50 


25 


1,740 


105.42 


30 


1,452 


88.00 


40 


1,089 


65.75 


50 


870 


52.71 


80 


54,5 


32.88 


100 


435 


26.36 


1.50 


290 


17.57 


200 


218 


13.18 



Under the influence of the drains the physical nature 
of the surface soil and of the subsoil gradually changes 
and undergoes improvement. Lines of seepage develop, 



648 SOILS: PROPERTIES AND MANAGEMENT 



and the drain gradually increases in efficiency. In heavy 
soil and in soils having hardpan properties, several seasons 
may be required for this change in the soil to spread 
three or four rods from the drains. The problem is to 
remove the excess water from the soil at the maximum 
distance from the drains in time to avoid serious injury 
to the crop. 

550. Construction of drainage trenches for tile. — 
Trenches' should be as small as possible and yet i)ermit 
the ready introduction of the tile. Unless the tiles to be 
used are of the larger sizes, the ditch should be made 
from twelve to fourteen inches wide, with vertical sides. 
Where leveling instruments are employed, the course 
of the ditch is staked out and the grade cord is stretched 
a definite distance above the proposed grade line of the 
ditch, to guide the workmen. In hand digging, the earth 
is thrown out with a narrow-pointed spade, the loose earth 




Fig. 66. — Tools for ditchiiiK. (1) and (2), ditching spades for remov- 
ing the major inirt of the earth from the ditch ; (3), grading scoop 
used to finish the bottom of the ditch and the grade; (4), skek^ton 
spade adapted for use in very phistic soil ; (5), shovel for removing 
loose earth; (6), hook used to place tile in deep, narrow trenches; 
(7) , pick for loosening stone and hard earth. 



LAND DRAINAGE 649 

is cleaned out with a round-pointed shovel, and the bottom 
is finished to a smooth, perfect grade by means of the 
grading scoop, which also rounds the bottom of the trench 
into shape to receive the tile. ( See Fig. 66. ) Care 
should be taken not to excavate the trench below the 
grade line, so that the tile may have a firm bed. 

Horse and engine power are now very generally applied 
to trench digging. Several types of plows drawn by 
horses are available to loosen the soil, and some types 
are arranged to follow the grade and to elevate the loose 
earth out of the trench. Several types of engine-driven 
machines are in use where tiie land is not excessively 
stony. They cut the trench to the full depth at one 
operation, and are constructed so as to follow a perfect 
grade, so that tile may be laid as fast as the machine 
progresses. 

551. Laying tile. — Where two lines of tile join they 
should come together at an acute angle, forming a Y 
so that the two streams of water will have the minimum 
interference and the collection of sediment will be pre- 
vented. If the lines are arranged at right angles, one of 
the strings may be turned down grade in the form of a 
curve in the last rod of its course, to make the proper 
union. Junction pieces or Y's may be bought in the 
smaller size of tile. They are rated by the diameter of 
the lateral and main branches ; for example, a 3 X 6 
junction indicates a three-inch lateral and a six-inch 
main. A lateral tile should enter the main drain with a 
slight drop. A small tile should enter a larger main 
drain at the horizontal center of the latter. 

The tiles are placed in the trench by hand, or, if the 
trench is deep or the tiles are very large, by means of 
some mechanical arrangement such as a hook. Their 



650 SOILS: PROPERTIES AND MANAGEMENT 

ends are put in line and as close together as conditions 
seem to indicate is necessary. Any covering or filling 
material is then put in place. The tile should be placed in 
the trench as soon as the latter is finished, and the trench 
should then be at least partially filled with earth in order 
to avoid danger from freezing or from the ca\ing-in of 
the walls. The first lot of earth — usually from the sur- 
face — is carefully placed about the tiles and packed 
in so as to hold them in position. This is called the 
blinding, or back-filling. The later filling may be accom- 
l)lishc(l in any convenient way. 

552. Size of tile. — The size of tile must be deter- 
mined by tlie amount and rate at which the water must be 
removed, tlie grade of the drain, and the nature of the 
soil. The small lateral drains whose function is to collect 
the water from the soil will usually be of three or four 
inches internal diameter. Drains smaller than this 
should not be used because of their inclination to become 
clogged. Small tiles are relatixely more aft'ected than 
larger tiles by the inevitable slight imperfections in the 
grade. The high friction of the walls in small tiles to 
the moving water reduces the rapidity of flow and en- 
courages the accumulation of sediment. In soil some- 
what of the nature of (juicksand, and where the grade is 
less than one foot in a hundred, no tile smaller than four 
inches in diameter should be used. As the drainage 
water is collected by the difi'erent lines, the size of the 
tiles must hicrease correspondingly. 

553. Amount of water to be removed from land. — 
]\Iany things afi'ect the amount of water to be removed 
from a given area of land. , The more important of these 
are the rainfall, the occurrence of springs, surface accu- 
mulation, tlie storage capacity of the soil, and rate of 



LAND DRAINAGE 651 

evaporation. Underd rains are designed with a capacity 
to remove only part of the normally largest rainfall 
in a period of twenty-four hours. The absorptive 
power of the soil and its hindrance to the flow of 
water through its pores permits the use of a tile-drain 
system capable of removing from one-quarter to one- 
half inch of water over the drainage basin in twenty- 
four hours. This is termed the drainage coefficient of the 
area. The drainage coefficient of the system, especially 
if it is a large system, should be determined after careful 
study of the amount and distribution of the rainfall 
and the extent to which surface and subterranean water 
is accumulated. 

554. Carrying capacity of a tile-drain system. — The 
carrying capacity of a system of tile drains depends on 
their respective sizes, their grade, or fall, their total length, 
their depth in the ground, the straightness of their course, 
and the smoothness of the interior of the tile. Some of 
these factors affect the flow directly as they increase, 
others inversely. The two most important elements 
in determining the capacity of a drain are the diameter 
and the grade. The capacity of a drain varies as the 
square of the diameter. Doubling the grade increases 
the capacity by approximately one-third. With cer- 
tain additional corrections and modifications, all the 
factors that affect the flow have been put together in a 
formula to determine the necessary size of the outlet 
tile for a given area. This formula, known as Ponce- 
let's formula, as modified by P^lliott^ for large systems, 
is as follows : — 



1 Elliott, C. G. Engineering for Land Drainage, Chapters 
VII, VIII, IX. New York. 1912. 



d{h + I) + ^ K 



652 SOILS: PROPERTIES AND MANAGEMENT 

(1) A=^ 

C 

(2) Q = a\ 

(3) V ^ 48^, 

yl = acres to be drained 

C = coefficient of drainages selected for the area in 
cubic feet per second. It is determined by 
the depth of water to be removed in twenty- 
four hours 

Q = quantity of water the tile will discharge, in 
cubic feet per second 

a = area of tile in square feet 

V = velocity in feet per second 

d = diameter of tile in feet 

/ = length of tile in feet 

h = head, or difference in elevation between outlet 
and upper end, in feet 

b = sum of amounts of head in laterals, in feet 

n = luimber of laterals 

A'^ = depth of tile below soil surface at upper end, in 
feet 

48 and 54 are factors that take account of gravity, 
• the size of the tile, and the roughness of the 
walls. The former figure is larger for tile 
more than twelve inches in diameter. 

The first formula determines the number of acres that 
a given size of tile will drain, by dividing the quantity 
of water to be removed by the coefficient of drainage 
selected for the region. 



LAND DRAINAGE 



653 



The second formula determines the quantity of water 
possible to remove, by muhiplying the area of the cross 
section of the tile by the velocity of flow. 

The third formula is used to determine the velocity of 
flow of water in the outlet tile. 

In a small system, where the laterals are relatively 
unimportant and where the soil is fairly close, the velocity 
formula may be much simplified as follows : — 



F = 48 



dh 



\+bU 



The term ^ K is used only where the soil is so very 
porous that the ready movement of the water through 
the soil has an influence on the flow in the tile. 

Coefficients of. drainage and their equivalents in cubic 
feet per second of discharge are as follows : — 



Depth op Water in Inches Removed 
IN Twenty-four Hours 


Cubic Feet to a Second op Dis- 
charge 


Fraction 


Decimal 


To an Acre 


To a Square Mile 


1 

3 

4 

1 
4 


1.00 
0.75 
0.50 
0.25 


0.0420 
0.0315 
0.0210 
0.0105 


26.9 

20.2 

13.4 

6.7 



From the above formula Elliott has calculated the 
number of acres of land drained by outlet tiles of different 
sizes and grades where the coefficient is one-fourth of an 
inch in twenty-four hours and where the main i^ 1000 
feet in length : — 



654 soils: properties and management 



Acres from which a Main Tile Laid on Grades Indicated 
MAY Adequately Receive Drainage Water 



Diameter 

OP Tile 

(in Inches) 


Grades to a Hundred Feet in Decimals op a Foot with 
Approximate Equivalents in Inches 


J inch 


1 inch 


2 inches 


3 inches 


6 inches 


9 inches 




0.04 


0.08 


0.16 


0.25 


0.50 


0.75 


5 
6 

7 

8 

9 

10 

12 


Acres 

17.3 
27.3 
39.9 
55.7 
74.7 
96.9 
152.2 


Acres 

19.1 
29.9 
44.1 
61.4 
82.2 
106.7 
167.7 


Acres 
22.1 
34.8 
51.1 
71.2 
95.3 
123.9 
194.6 


Acres 

25.1 

39.6 

58.0 

80.9 

108.4 

140.6 

221.1 


Acres 

32.0 
50.5 
74.5 
103.3 
138.1 
179.2 
281.8 


Acres 

37.7 
59.4 
87.1 
121.4 
162.6 
211.1 
331.8 



555. Cost of drainage. — The cost of tile drainage 
depends on many things, including especially the size of 
the tile, the frequency of the drains, the depth, the nature 
of the soil, the method of digging, and the price of labor. 
The co.st of tile varies in d liferent regions and increases 
rapidly with the size. 

The following schedule will serve merely as a general 
guide to the range in price a thousand feet and a rod when 
purchased in car lots : — 







Size (Diameter in Inches) 




2 


3 


4 


5 


6 


8 


Cost a thousand 

feet .... 

Cost a rod . . 


$ 10- $14 
$.16-$.21 


$ 13-$ 18 
$.20-$.27 


$ 18-$ 25 
$.27-$.38 


$ 25-$ 32 
$.38-$.48 


$ 35-$ 45 
$.53-$.68 


$65-$80 
$.98-$1.12 



The. cost for digging the trench of course varies widely. 
In medium soil free from stone, for a ditch two and one- 



LAND DRAINAGE 



655 



half feet deep to receive tile up to ten inches in diameter, 
the cost may be from fifteen cents to fifty cents a rod, 
with an average of about thirty-five cents. The cost can 
sometimes be reduced by the use of a power machine. 
In stony and hardpan soil the cost may be very much 
higher than these estimates. The deeper trench is rela- 
tively the more expensive to construct. 

Laying the tile, filling the trench, and other miscel- 
laneous operations for the smaller sizes of tile will cost 
at least ten cents a rod. This makes a total cost for four- 
inch tile of about 80 cents a rod, $5 a hundred feet, and 
$260 a mile. 

Records are available of the cost of drainage on an 
extensive area of cultivated farm land in northern Ohio,^ 
where the soil is chiefly a medium clay loam, somewhat 
stony, and where the depth was t\vo to three and one-half 
feet. Some of the work was done by hand and some with 
the aid of a traction ditching machine. A fairly low price 
prevailed for tile, the size ranging from three to thirteen 
inches. 

The results are as follows : — 



Area (in acres) 

Number of rods of tile . . . , 
Cost of installation per rod . 
Average cost of tile per rod . 
Average number of rods to the acre 
Average cost to the acre . . . 



Cost op Installing Tile 


Drains 


Hand work 


Machine work 


40 


188 


2,560 


8,835 


$0.4489 


10.3746 


$0.2445 


$0.2445 


48 


48 


$33.28 


$29.72 



1 Goddard, L. H., and Tiffany, H. O. The Cost of Tile 
Drainage. Ohio Agr. Exp. Sta., Circ. 147. 1914. 



656 SOILS: PROPERTIES AND MANAGEMENT 

556. Storm channels. — Where large volumes of water 
must be carried for a short time in addition to the normal 
flow, a medium-sized tile drain may be combined with an 
open surface channel for carrying away the flood water. 
The open channel is located a little to one side of the 
tile drain so that the latter may not be displaced by pos- 
sible erosion. The open surface channel is made broad 
and shallow in order to avoid interference with tillage 
operations, and if erosion is likely to occur, it may be 
kept in grass. 

557. Silt basins. — Silt basins are wells in the line 
of tile drains, for collecting sediment that might other- 
wise be deposited in the tile. The course of the drain 
is intercepted and a small well is sunk two or more feet 
below the bottom of the drain. The well extends to the 
surface of the ground and has a cover. The inlet drains 
come in at a slightly higher level than the outlet. The 
heavy sediment drops to the bottom, whence it may be 
removed from time to time. The end of the outlet tile 
is finished with an elbow, turned down so as to prevent 
the entrance of sticks or other floating material. The 
walls of the well may be made of wood, concrete, or 
brick. 

558. Surface intakes. — The admission of surface water 
into a tile drain should always be managed with great 
care to remove the hea\'ier sediment or other material 
that might obstruct the tile. Screen boxes should be 
used. The screen should incline to the intake at an angle 
of fifty or sixty degrees, so that floating material, instead 
of obstructing the flow, will be pushed upward out of the 
course. 

559. Outlets. — As few outlets as is practicable should 
be constructed for tile drains, and these should have a 



LAND DRAINAGE 



657 



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Fig. 67. — A drainage plan of an arna of land exhibiting many differences 
as to soil, slope, and degree of wetness. Herein are shown the kinds, 
sizes, and arrangements of drains necessary to provide efficient 
drainage under the various conditions. 



2u 



658 SOILS: PROPEBTIES AND MANAGEMENT 

drop and be well protected by wing walls. Lines of 
drains should be connected in systems for this puri)ose. 
Unless the drain has a high grade the outlet should not be 
covered by water. The end of the tile should be pro- 
tected by a gate or a series of rods to prevent the entrance 
of small animals. 

560. Muck and peat soil. — Muck and peat soil should 
usually be drained by open ditches at first. After learn- 
ing the nature of the material and the structure of the 
subformation, it may be found permissible to install tile 
in the smaller ditches. When the organic material is 
more than four feet deep, so that tile could not be laid 
on a hard bottom, much risk is involved in its use due 
to the excessive shrinkage of such soil when the surplus 
water is removed and when even moderate drying occurs. 
If the area is fed by springs so that the water level will 
be kept permanently at the base of the tile, the shrinkage 
will be very small and the tile may usually be laid with 
safety, especially if placed on boards to aid in keeping 
the alignment. In so-called dry peat, where the subsoil 
may dry out seriously in summer, the use of tile is inad- 
visable. In muck soil, which has a finer texture resulting 
from a more advanced stage of decay, tile drains may be 
used with greater safety. 

The distance between drains in muck should be from 
one hundred to five hundred feet, depending much on 
the nature of the subsoil. Since the surface is likely to 
be relatively flat, nothing smaller than four- or five-inch 
tile should be employed and the joints should be carefully 
protected as described above. 

Since the capillary power of muck soil is low, the water 
table should not be lowered more than from two to three 
feet, depending on the quality of the soil. While the 



LAND DRAINAGE 659 

bottom of the open ditch may go below this level, it is 
often advisable to insert check gates to hold the water 
level when it has been lowered to the desired depth. 

561. Drainage of irrigated and alkali lands. — Exces- 
sive irrigation and the occurrence of underground seep- 
age has resulted in the water-logging of extensive tracts 
of arid and semiarid land, and in the serious accumulation 
of alkali salts in the surface soil. An effective remedy 
for this condition is the installation of a thorough system 
of drains,^ preferably underdrains, coupled with heavy 
irrigation by means of which the excess salt is leached out 
in the drainage water. The most seriously alkaline land 
is now being effectively reclaimed by drainage, for the 
production of alkali-sensitive crops. 

For this purpose drains are installed deeper than is the 
custom in humid regions, in order to reduce the capillary 
rise of moisture to the surface of the soil, where the alkali 
salts are deposited in injurious amounts. The drains 
are often placed at depths of from four to six feet. Special 
care is also taken to intercept the underground seepage. 
Sometimes the seepage water from leaky canals and reser- 
voirs and from over-irrigation may pass long distances 
in porous gravel strata and rise to the surface of the land 
on encountering some impervious obstruction. In such 
cases wells may be sunk many feet to the water-bearing 
stratum, and the water thus conducted away in drains 
far enough below the surface to avoid injury to the soil. 

Many special problems are encountered, such as the 
occurrence of hardpan — usually a stratum cemented by 
alkaline carbonates — and the development of a serious 

> Elliott, C. G. Development of Methods of Draining Irri- 
gated Lands. U. S. D. A., Office Exp. Sta., Ann. Rept., 
pp. 489-501. 1910. 



660 SOILS: PROPERTIES AND MANAGEMENT 

quicksand condition of soil. The hardpan may need to 
be partially broken up by dynamite. The latter condi- 
tion may require the placing of the tile on boards or the 
use of wooden box drains to keep the alignment. 

Coupled with deep drainage, sufficient irrigation water 
is employed to produce heavy percolation, by means of 
which the excess salt is removed. The most alkaline 
land can usually be reclaimed in two or three years of 
leaching. 

562. Vertical drainage. — A gravity outlet for drainage 
is sometimes difficult to provide. In such a case it may 
be possible to remove the drainage water through some 
porous stratum below the surface. There must be such 
a porous stratum within reach below the surface, in order 
to render the method of vertical drainage practicable. 
Basin-shaped areas without an outlet may be wet because 
of the accumulation of a thin layer of clay or other im- 
pervious sediment in its lowest part, beneath which at 
a short distance is a porous gravel or sand formation. 
Anything that perforates this impervious layer and keeps 
open the passage will afford drainage. Wells several 
feet in diameter may be cpnstructed and filled with stone. 
Tile drains and open drains have been emptied into such 
structures. An opening of temporary efficiency may be 
formed by a charge of dynamite. The tendency of such 
an opening, however, is to become clogged. 

A second condition under which vertical drainage may 
be advisable exists in a soil that is underlaid within a few 
hundred feet by a limestone or other porous rock forma- 
tion into which the surface water may be emptied. A 
casing may be installed to protect the walls of the well 
and to reach from the surface to the porous stratum. 
In addition a trapped intake, coupled with a silt basin, 



LAND DRAINAGE 661 

may be placed at the top of the well to insure its continu- 
ous operation. Extensive systems of underdrains are 
reported to have been discharged by this arrangement, 
where it might otherwise have been necessary to go a 
long distance in order to obtain an outlet. It should be 
noted that in many cases a sufficiently porous stratum 
is lacking in the structure of the surface portion of the 
earth, so that the method could not often be employed. 

563. Drainage by means of explosives. — The use of 
explosives for proriioting drainage has been proposed 
for three conditions : — 

1. To break up a hard subsoil and possibly make a 
connection with a more porous stratum below, so that the 
soil could better handle the normal rainfall. This is 
closely related to the operations of subsoiling. 

2. To break through a thin impervious layer in the 
bottom of a Avet basin-shaped area. This is identified 
with vertical drainage described above. 

3. To open up channels for drainage purposes. This 
use is the most extensive. By proper distribution of the 
charges of explosives, coupled with favorable soil and 
weather conditions, a very good channel can be opened 
by this method. It is suited only to the excavation of 
open ditches of medium size, three feet or more in width, 
and it has the greatest advantages where the land is 
much obstructed by stone or stumps. The force of the 
explosive largely clears the ditch of earth and obstructions. 
No very accurate grading of the bottom of the ditch can 
be accomplished by this method. 

564. Resume. — The removal of the excess water 
from the soil by any means constitutes drainage and is 
one of the most fundamental operations in soil manage- 
ment. The effects of adequate drainage are numerous 



662 SOILS: PROPERTIES AND MANAGEMENT 

arid far-reaching. In its accomplishment the physical 
properties of the soil and its moisture relations must be 
taken into account. Whether open ditches or under- 
drains are employed depends on the local conditions, but 
where practicable underdrains are always to be chosen. 
While the cost of drainage is a considerable sum, the 
improvement when well made is of long duration and the 
cost may therefore be distributed over a long period. 
The benefits accrue not only in increased crops, which 
are generally large, but also in the saving of expense in 
operation. Good drainage is the basis of good soil 
management. 



CHAPTER XXIX 
TILLAGE 

While the farmer depends somewhat largely on the 
weathering agencies for granulation of his soil, maximum 
tilth can be obtained only by certain external operations. 
The advantages to be derived from drainage have been 
pointed out. The importance of the addition of lime 
and organic matter as a means of soil improvement has 
been emphasized. Yet, after all these have been pro- 
vided, a further fundamental practice remains to be 
followed. This practice is tillage, or the manipulation 
of the soil by means of implements so that its struc- 
tural relationships may be made better for crop growth. 
Tillage is so general in its application, so pronounced in 
its effects, and so complex in its modes of operation, and 
has to do with so many machines employing different 
mechanical principles, that it requires discussion by itself. 

565. Objects of tillage. — Tillage aims to accomplish 
three primary purposes: (1) modification of the struc- 
ture of the soil ; (2) disposal of rubbish or other coarse 
material on the surface, and the incorporation of manures 
and fertilizers into the soil ; (3) deposition of seeds and 
plants in the soil in position for growth. 

The most prominent of these purposes is the modifi- 
cation of the soil structure. This afi'ects the retention 
and movement of moisture, aeration, and the absorption 
and retention of heat, and either promotes or retards the 

663 



664 SOILS: PROPERTIES AND MANAGEMENT 

growth of organisms. Through all these factors the com- 
position of the soil solution, and finally the penetration 
of plant roots, is influenced. The creation of a soil 
mulch is merely a change in the structure of the soil at 
such times and in such a manner as will prevent evapora- 
tion of moisture. For this reason it is essential to under- 
stand the relation of soil structure to the movement of 
moisture in managing the mulch. In fine-textured soils, 
in which the granular or crumb structure is most desired, 
tillage may have an important influence on the formation 
or destruction of granules. As has been pointed out, 
any treatment that increases the number of lines of weak- 
ness in the soil structure facilitates the action of the mois- 
ture films and the colloidal material in solidifying the 
soil granules. Tillage shatters the soil and breaks it into 
many small aggregates which may be further drawn 
together and loosely cemented as a result of the evapo- 
ration of moisture. The more numerous the lines of 
w^eakness produced, the more pronounced is the granu- 
lation ; and, conversely, the fewer the lines of weakness 
produced, the more coarse and cloddy is the structure. 

566. Implements of tillage. — The implements adapted 
to the manipulation of the soil are very numerous, and 
embrace many types. Many operations are compre- 
hended by the term tillage, which includes the use of all 
those implements that are used to move the soil in any 
way in the practice of crop production. It includes the 
smallest hand implements as well as the heaviest trac- 
tion machinery. 

567. Effects on the soil. — All these operations may 
be divided into two groups, according to their efl'ect on 
the soil, — those that loosen the soil structure, and those 
that compact the soil structure. In the subsequent 



TILLAGE 665 

paragraphs of this chapter the effect of the commoner 
types of tillage implements on the soil are pointed out 
as a guide to their selection for the accomplishment of 
a desired modification. Good soil management consists, 
first, in analyzing the soil conditions, in order to deter- 
mine the change that should be effected ; and second, in 
the selection of the implement or other treatment that 
will most readily and economically accomplish the object. 

568. Classes of tillage implements. — According to 
their mode of action, tillage implements may be divided 
into three groups, — plows, cultivators, packers and 
crushers. 

569. Plows. — The primary function of a plow is to 
take up a ribbon of soil, twist it upon itself, and lay 
it down again bottom side up, or partially so. In the 
process two things result : (1) if the soil is in proper condi- 
tion for plowing, it will be shattered and broken up ; 
(2) the soil is partially or wholly inverted, and any rubbish 
is put beneath the surface. 

570. Pulverizing action of the plow. — In twisting, the 
soil tends to shear into thin layers, as already pointed 
out (par. 128). These layers are moved unequally upon 
each other, as the leaves of a book when they are bent. 
The result should be a very complete breaking-up of the 
soil. How thorough the breaking-up will be will depend 
on (1) the condition of the soil, and (2) the type of plow. 
As to the condition of the soil, there is a certain optimum 
moisture content at which the best results w^ill be obtained. 
That condition of moisture is the one that is best for 
plant growth. Any departure from this optimum moisture 
content will result in less efficient work. It has been said 
that, in proportion to the energy required, the plow is 
the most efficient pulverizing implement used by the 



666 SOILS: PROPERTIES AND MANAGEMENT 

farmer. The optimum moisture content for plowinji^ is 
indicated by that moist state in which a mass of the soil, 
when pressed in the hand, will adhere without puddling 
but may be readily broken up without injury to the 
intimate soil structure. This is a much more critical 
stage for fine-textured soils than for coarse-textured ones. 
Sandy soils are not greatly altered by plowing when out 
of optimum moisture condition. On the other hand, if 
a clay is plowed when it is saturated with water, it will 
be thoroughly puddled and will dry out into a hard, lumpy 
condition. Such a structure requires a considerable time 
to remedy. 

571. Types of plows (Fig. 68). — There are two gen- 
eral types of turning plows, the common moldboard plow 
and the disk plow. Their mode of action is quite dif- 
ferent, although, so far as the soil is concerned, the result 
is much the same. The moldboard plow seems to have 
a wider application than the disk plow, but both have 
a particular sphere of usefulness. 

The disk plow is essentially a large revolving disk 
set at such an angle that it cuts off and inverts the soil, 
at the same time pulverizing it fairly effectively after 
the manner of the moldboard plow. One advantage 
claimed for the disk plow is its lighter draft for the same 
amount of work done, due to its having rolling friction in 
the soil instead of sliding friction. In practice it appears 
to be especially effective on very dry, hard soil and in 
turning and covering rubbish. 

For any given texture of soil and any given soil condi- 
tion, there is a type of plow, a shape of moldboard, and 
a depth of furrow slice, that will give the best results. 
This fact is to be kept constantly in mind in plowing soil. 
Sod land requires a different shape of plow from fallow 



TILLAGE 



667 



land, sandy land from clay land. Rubbish on the surface 
may be handled by one plow and not by another. On 
wet clay one should use a different shape of plow from 
that which is preferable for dry soil. 




Fig. 68. — The plow. (1), modern walking plow with parts named; 
(2), types of moldboard for (a) fallow ground, light soil, (b) fallow 
ground, clay soil, (c) sod ground, (d) general purpose, fairly well 
suited to a wide range of soil conditions ; (.3), deep-tilling disk plow ; 
(4), subsoiler ; (5), plow attachments: (a) jointer, (6) knife or 
beam colter, (c) fin colter, (d) rolling colter. 



572. Shapes of moldboard plows. — Of the moldboard 
type there are two general shapes: (1) The long, sloping 
moldboard, w'hich rises very gradually and has little or 



668 SOILS: PROPERTIES AND MANAGEMENT 

no overhang, found on what is called the sod plow. This 
neatly cuts ofT the roots at the bottom of the slice, slowly 
and gradually twists the soil over without breaking the 
sod, and lays it smoothly up to the previous furrow slice. 
(2) The short, steep moldboard with a marked overhang. 
This is not adapted to sod land, because it breaks up 
the sod and shoots it over in a rough, jagged manner 
with une\en turning. But on fallow land, to which it 
is adapted, it very completely breaks up the soil and 
throws it over in a nearly level, mellow mass. The pul- 
verizing effect is obviously much greater than with the 
sod plow. Since the steep moldboard, or fallow-ground, 
plow exerts the most force on the soil in a given time at 
a given speed of movement, it follows that if a particular 
soil is over-wet it should be plowed with the sod plow ; 
while, if it must be plowed when too dry, the fallow-ground 
plow will be more effective — disregarding the draft, 
which will probably be larger in the latter case. 

573. Position of the furrow slice (Fig. 69). — Con- 
siderable care should be taken concerning the angle at 
which the furrow slice is placed. It is seldom desirable 
to completely invert the soil. If it is too fiat, the stubble 
and rubbish are matted at the bottom of the furrow and 
tend to interfere with capillary movement for a consid- 
erable period. This may cause serious difficulty on 
spring-plowed soil, where the capillary connection does 
not have time to be renewed before a crop occupies the 
land. If, on the other hand, the furrow is too steep, the 
proper pulverization does not take place and the turning- 
under of stubble and rubbish is not satisfactorily accom- 
plished. The stubble and rubbish are likely to interfere 
with subsequent operations. 

The best angle at which to turn the furrow slice is 



TILLAGE 



669 



about from 30° to 40° with the horizontal. A furrow thus 
set furnishes ready entrance for rain water and facihtates 
the best of aeration for the soih Such an angle is espe- 
cially to be recommended for turning under green manures. 
The capillary connections with the subsoil are not broken 
and the green material is well distributed from the top 
to the bottom of the furrow. Where a sod is to be plowed, 
a flatter turning of the furrow is advocated in order to 
increase the packing and avoid the danger of the sod's 
interfering with subsequent cultivation. 




Fig. 69. — Section of plowed land showing the correct proportions and 
position of the furrow slice as left by a moldboard plow. The effect 
of the jointer in turning under the edge of the furrow slice as well 
as the position of turned under vegetation is apparent. 



574. Depth and width of furrow. — There is a general 
relation between the width of the furrow slice and its 
depth. In general, it may be said that this ratio is about 



670 SOILS: PROPERTIES AND MANAGEMENT 

two in width to one in depth. The greater the depth, the 
less in proportion may be the width of the furrow slice. 

On clay soil in particular, there is also a relation be- 
tween depth and condition. A wet soil should be plowed 
more shallow, other things being equal, than a dry soil, 
because the puddling action is less. On a dry soil the 
depth should be increased, in order to increase the pul- 
verization. Combining these principles, then, it may be 
said that if a clay soil must be plowed when too wet, it 
should be plowed with a sod plow and to as shallow a 
depth as is permissible. But on an over-dry soil the 
opposite conditions should be fulfilled — that is, the use 
of a steep moldboard and to an increased depth. Like- 
wise, on sandy soil, where the aim is generally to compact 
the structure, this may be furthered by deep plowing 
with a steep moldboard when the land is over-wet. 

575. Plow sole. — In connection with this phase of 
the subject it is important to consider what is often called 
the " plow sole," — that is, the soil at the bottom of the 
furrow, which bears the weight of the plow and the tram- 
pling of the team, and which under a uniform depth of 
plowing does not become loosened. In clay soil, espe- 
cially, it gradually becomes more compact, developing 
in time something of a hardpan character, which is detri- 
mental to the circulation of air and moisture and inter- 
feres with the penetration of plant roots. Consequently, 
occasional deep plowing, or even subsoiling, is recom- 
mended to break up this unfavorable soil structure. 
There is less tendency for the disk plow than for the mold- 
board plow to form the " sole." 

576. Hillside plow. — The hillside plow is a modified 
form of the moldboard plow. It has a double curvature 
to the moldboard, so that it is essentially two plows in 



TILLAGE 671 

one. The plow swings on a swivel in such a way that 
it may be locked on either the right or the left side. It 
removes the necessity of plowing in beds, and, by per- 
mitting all the work to be done from one side, enables 
the plowman to lay the furrow slices in one direction. 
On the hillside this direction is down the slope, because 
of the greater ease in turning the soil in that direction. 
This plow also removes the difficulty of pulling up and 
down the hill. There is another type of moldboard plow, 
designed to eliminate " dead furrows " and " back fur- 
rows." Dead furrows are developed by the last furrow 
slices of two lands being turned in opposite directions, 
thereby leaving a gulley between, which is often unpro- 
ductive in character ; the back furrow consists of two 
furrow slices thrown together, usually forming a ridge 
more productive than the average of the land. This 
plow is of the sulky type, the plow being carried on wheels 
and regulated by means of levers and the traction power. 
Two plows are carried, one having a right-hand turn to 
the moldboard, and the other a left-hand turn. By 
using one plow in one direction and the other in the oppo- 
site direction, it is possible to begin on one side of the field 
and throw the furrow slice in one direction until the 
entire area is covered, thereby leaving the soil in a uni- 
form condition. Such plows, being heavier than the 
single, walking plow, are not adapted to very uneven 
ground. 

577. Covering rubbish. — The secondary function of 
the plow is to cover weeds, manure, and rubbish that 
may be on the surface. This also the turning plow 
does very effectively. The cutting and turning of the 
sod, rubbish, and weeds is facilitated by several attach- 
ments, such as colters, jointers, and drag chains. There 



672 soils: properties and management 

are several types of colters. Blade colters are attached 
to the beam or to the share in such a manner as to cut 
the furrow slice free from the land side. They should 
be adjusted in such a position as to cut the soil after it 
has been raised and put in a stretched condition, at which 
time the roots are most easily severed. This position is a 
little back of the point of the share. A knife edge attached 
to the share is commonly called a fin colter. A jointer 
is a miniature moldboard attached to the beam for cutting 
and turning under the upper edge of the furrow slice, 
so that a neat, clean turn is effected without the exposure 
of a ragged edge of grass which may continue growth. 
This is used chiefly on sod land. A drag chain is an ordi- 
nary heavy log chain, one end of which is attached to 
the central part of the beam and the other to the end of 
the double tree on the furrow side, and with enough slack 
so that it drags down the vegetation on the furrow slice 
just ahead of the turning point. It is used primarily in 
turning under heavy growths of weeds or 'green-manure 
crops. 

578. Subsoil plow. — There is a third type of plow, 
the so-called subsoil plow. The purpose of this imple- 
ment is to break up and loosen the subsoil without mix- 
ing the material with the soil. It consists essentially of a 
small, molelike point on a long shin. This implement is 
drawn through the bottom of the furrow, and shatters 
and loosens the subsoil to a depth of IS inches or 2 feet. 
It is often useful on soils having a dense, hard subsoil. 
Its use requires the exercise of judgment, as the process 
may prove very injurious if done out of season. As a 
general rule, it is best to use the subsoil plow in the fall, 
when the subsoil is fairly dry and may in a measure be 
recompacted by the winter rain. Spring subsoiling is 



TILLAGE 673 

seldom advisable in humid regions, owing to the danger 
of puddling the subsoil, or to the possibility of its remain- 
ing too loose for best root development if the work is done 
when the subsoil is dry enough not to puddle. 

579. Cultivators ( Fig. 70 ) . — There are more types 
of cultivators than of any other form of soil-working im- 
plements. These may be grouped into (1) cultivators 
proper ; (2) leveler and harrow types of cultivators ; (3) 
seeder cultivators. These implements agree in their mode 
of action on the soil, in that they lift up and move it side- 
wise with a stirring action which loosens the structure and 
cuts off weeds, and to a slight degree covers rubbish. How- 
ever, the action is primarily a stirring one, and, in general, 
it is much shallower than that of the plow. One impor- 
tant fact should be kept in mind in cultural operations, 
especially those just following the plowing ; that is, the 
work should be done when the soil is in the right moisture 
condition. Particularly is this true in the pulverization 
following the plowing. Plowing, if it is properly done, 
leaves the soil in the best possible condition to be further 
pulverized. It is properly moistened, and if the clods 
are not shattered they are reasonably frail and may be 
much more readily broken down than when they are 
permitted to dry out. In drying they are somewhat 
cemented together and thereby hardened. Not only is 
it desirable in almost all cases to take advantage of this 
condition of the soil, but the leveling and pulverizing 
of the soil reduces drying and improves the character of 
the seed bed. 

580. Cultivators proper. — There is a great variety 
in types and patterns of cultivators. They may be 
divided into large shovel forms and small shovel forms, 
and the duck-foot form. The first type has a few com- 

2x 



674 SOILS: PROPERTIES AND MANAGEMENT 



paratively large shovels set rather far apart, which vigor- 
ously tear up the earth to a considerable depth and leave 
it in large ridges. There is a lack of uniform action, and 
the bottom of the cultivated part is left in hard ridges. 
Such implements are now much less used than they were 
formerly, and may be considered to supplant in a measure 
the use of the plow, where deep working without turning 




Fig. 70. — Tyi^os of cultivators: (1), wlu'cl hoc, or hand Rardcn culti- 
vator, with attachments; (2), adjustable small-tooth, ouc-horso 
cultivator, with duck-foot shovel behind; (3), two-horse spring- 
toothed cultivator; (4), two-horse sweep or knife cultivator; 
(5) , two-horse disk cultivator. 



TILLAGE 675 

is desired. Some of the wheel hoes used in orchard 
tillage belong to this type. The single and double shovel 
plows are earlier types of the same implement. 

The small shovel cultivators have very generally sup- 
planted the large shovel type in most cultural work. 
The decrease in size of shovels is made up by the great 
increase in number. Ordinarily they operate to shallow 
depths, but very thoroughly and uniformly. They are 
now much preferred in all intertillage work for eradication 
of small weeds and the formation of a loose surface mulch. 

The duck-foot cultivator — or sweep as it is called in 
the southern states, where it is extensively used in the 
cultixation of cotton — is a broad blade that operates 
in a nearly horizontal position an inch or two beneath the 
surface. The surface layer of soil is severed and raised 
slightly from the under soil, and is somewhat crumbled 
in the operation. This tool is very efficient in establishing 
and maintaining a mulch and in destroying weeds. It 
covers every part of the soil. The implement is increasing 
in popularity in the northern and eastern states. It is 
not adapted for use in very stony or hard soil. 

Another classification, which has less relation to utility 
than to the convenience and comfort of the operation, 
is based on the presence or the absence of wheels. There 
is a strong movement toward the use of wheel cultivators 
carrying a seat for the operator. These have a wider 
range of operation as to depth and facility of movement 
than have the cultivators without wheels. 

Still further, there is the distinction of shovels from 
disks. Disks are used on the larger cultivators but seldom 
on the small ones. 

Cultivators may be constructed to till one or more rows 
at a time. 



676 SOILS: PROPERTIES AND MANAGEMENT 

581. Leveler and harrow types of cultivator (Fig. 71). 
— Ill this group are the spike-tooth harrow, the smoothing 
harrow, the spring-tooth harrow, the disk harrow, the 
spading harrow, weeders, and the Acme and Meeker 
harrows. 

The spike-tooth harrow is essentially a leveling imple- 
ment, adapted to very shallow cultivation of loose soils. 
It is also something of a cleaner, in that it picks up surface 
rubbish. The spring-tooth harrow works more deeply 
than does the spike-tooth harrow, and can therefore be 
used in many soils for which the latter is not adapted. 
In working down cloddy soil it brings the lumps to the 
surface, where they may be crushed. The disk harrow 
depends for its primary advantage on the conversion of 
sliding friction into rolling friction. Its draft is therefore 
less for the same amount of work done. It has a vigorous 
pulverizing action similar to that of the plow, surpassing 
shovel cultivators in this respect. The disk harrow is 
not adapted to stony soil, but the toothed forms are as 
effective on such soil as on soil free from stones, as long 
as the stones are not large enough to collect in the imple- 
ment. On the other hand, on land full of coarse manure, 
sod, and the like, the disk harrow is the more efficient. 
The spading harrow (cutaway disk) is very little different 
from the disk harrow, except that it takes hold of the soil 
more readily. A recent attempt to bring about a high 
degree of pulverization, and with greater uniformity, is 
represented by the double-disk implements. In these 
implements there are two sets of disks, one set in front 
of and zigzagged with the other, and the two adjusted 
so as to throw the soil in opposite directions. 

Weeders are a modified form of the spring-tooth har- 
row, adapted to shallow tillage of friable, easily worked 



TILLAGE 



677 



soil, where the aim is to kill weeds and create a thin sur- 
face mulch. They are wide and are fitted with handles, 
and therefore have an intermediate place between culti- 
vators proper and harrows. They are much used for 
intertillage of young crops. 






Fig. 71. — Types of harrows: (1), spike-tooth; (2), spring-tooth; 
(3), weedor; (4), double disk (note that the forward disks are 
soHd while the rear disks are of the cut-out type) ; (5), spading 
disk ; (6) , Acme. All these belong to the cultivator group of im- 
plements. 



The Acme harrow consists of a series of twisted blades 
which cut the soil and work it over. They are most 
useful in the later stages of pulverization on soil relatively 
free from stones. The Meeker harrow is a modified form 
of disk, used primarily for pulverization. It consists of 
a series of lines of small disks arranged on straight axles, 
and is especially adapted to breaking up hard, lumpy soil. 



678 SOILS: PROPERTIES AND MANAGEMENT 

In this particular it may be considered as belonj^ing to the 
third set of implements, the clod crushers. But as com- 
pared with the roller on hard soil it is more efficient. 

582. Seeder cultivators. — Many implements used 
primarily for seeding purposes are also cultivators, and 
their use is equivalent to cultivation. The grain drill 
is a good example of this group. It is essentially a culti- 
vator — either shoe or disk — adapted to depositing the 
grain in the soil at the proper depth. All types of j)lanters 
that deposit the grain in the soil have a similar action 
on the structure of the soil. The ordinary two-row maize 
planter, the potato planter, and the like, while of low 
efficiency as cultivators, still have an effect which is 
measurable. This action is well seen in the lister, used 
for planting maize, by which the grain is deposited l)eneath 
the furrow, which is filled by cultivation after the grain 
is up. The lister is generally used without previously- plow- 
ing the ground, and its use is limited to regions of low rain- 
fall where the soil is aerated by natural processes. Plowed 
ground listers have lately been introduced, which com- 
bine the advantages of deep planting with proper prep- 
aration of the soil. 

There is also a very considerable tillage action in many 
harvesting implements. The i)otato digger, for example, 
very thoroughly breaks up and cultivates the soil, and 
this process is one important reason for the general 
high yield of crops following the potato crop. Bean 
harvesters and beet looseners also have a similar action 
on the soil. 

583. Packers and crushers. — These may be divided 
into two groups — those implements that aim to compact 
the soil, and those the primary purpose of which is to 
pulverize the soil by crushing the lumps. Both kinds 



TILLAGE 679 

of implements have something of the same action on the 
soil. That is to say, any implement that compacts the 
soil does a certain amount of crushing ; and, conversely, 
any implement that crushes the soil does some com- 
pacting. 

584. Rollers (Fig. 72). —The type of the first group 
is the solid, or barrel, roller, which by its weight tends to 
force the particles of soil nearer together and to smooth 
the surface. The smaller the diameter in proportion to its 
weight, the greater is the effectiveness of the roller. Its 
draft is correspondingly greater. As a crusher, the roller 
is relatively inefficient on hard, lumpy soil, because of its 
large bearing surface. Lumps are pushed into the soft 
earth rather than crushed. 

It should be mentioned that there is one condition 
under which the roller is effective in loosening up the soil 
structure. This is on fine soil on which a crust has 
developed as a result of light rainfall. Here the roller 
may break up the crust and restore a fairly effective soil 
mulch. 

Another form of roller is the subsurface packer. One 
type of this implement consists of a series of wheels with 
narrow, V-shaped rims, which press into the soil and com- 
pact it while leaving the surface loose. The wheels 
are designed primarily to smooth the land after plowing, 
and to bring the furrow slices close together and in good 
contact with the subsoil, in order to conserve moisture 
and promote decay of organic material that may be plowed 
under. This packer has been developed chiefly in semi- 
arid and arid sections of country where the conservation 
of moisture is especially important, but it might well 
have a much larger use for the same purpose in sections 
of the country that are subject to late summer and fall 



680 SOILS: PROPERTIES AND MANAGEMENT 

droughts. While compacting the soil, this implement 
leaves a mulch. 




mmummiim. 




Fig. 72. — Types of packers and pulverizers : (1), solid or barrel roller; 
(2) , corrugated roller ; (3) , crusher and subsurface packer ; (4) , 
bar roller. 

585. Clod crushers. — The aim of these clod crushers 
is to break up lumps. As to mode of action, there are 
several forms. The corrugated and the bar roller and 
the clod crusher concentrate their weight at a few points, 
and are open enough so that the fine earth is forced up 
between the bearing surfaces. They are very effective 
in reducing lumpy soil to comparatively fine tilth. They 
have very little leveling effect further than the breaking- 
down of lumps. 

The planker, drag, or float, variously so-called, con- 
sists essentially of a broad, heavy weight without teeth, 
which is dragged over the soil. The lumps are rolled 
under its edge and ground together in a manner which 
very effectively reduces their size. At the same time 
the soil is leveled, smoothed, and, to' a degree, compacted. 
This implement may well be used in the place of the roller 



TILLAGE 681 

as a pulverizer, on many occasions. It is constructed in 
many forms. 

586. Efficient tillage. — Efficient tillage requires an 
understanding of the properties of the soil, good practi- 
cal judgment as to its condition, facility in the selection 
of the proper implements for its modification, and me- 
chanical skill in their operation. The same result may 
often be attained in different ways, and the practical 
necessity that frequently arises for the farmer to get on 
with a relatively few tillage implements where a variety 
of soil conditions must be dealt with draws heavily on his 
resourcefulness. 



CHAPTER XXX 
IRRIGATION AND DRY-FARMING 

Irrigation ^ is the application of water to the soil for 
the purpose of growing crops. It is supplementary to the 
natural preci})itation. The quantity of water applied 
and the time of application must therefore be determined 
by the character of the rainfall. 

587. Relation of irrigation to rainfall. — The limit of 
rainfall where irrigation becomes necessary is not a fixed 

' Widtsoe, J. A. Principles of Irrigation Practice. New 
York. 1914. 

Olin, W. H. American Irrigation Farming. Chicago. 1913. 

Bowie, A. Practical Irrigation. New York. 1908. 

King, F. H. Irrigation and Drainage. New York. 1899. 

Paddock, W., and Whipple, O. B. Fruit (Growing in Arid 
Regions. New York. 1910. 

Newell, F. H. Irrigation. New York. 1902. 

Mead, E. Irrigation Institutions. New York. 1903. 

Mead, E. Preparing Land for Irrigation and Methods of 
Applying Water. U. S! D. A., Office Exp. Sta., Bui. No. 145. 
1904. 

Wickson, J. A. Irrigation among Fruit Growers on the 
Pacific Coast. U. S. D. A., Office Exp. Sta., Bui. No. 108. 
1902. 

Widtsoe, J. A., and Merrill, Tj. A. Methods for Increasing 
the Crop Producing Power of Irrigation Water. Utah Agr. 
Exp. Sta., Bui. No. 11(5. 1912. 

Fortier, S. The Use of Small Water Suiiiilies for Irrigation. 
U. S. D. A., Yearbook, p. 409. 1907. 

Fortier, S. Irrigation of Orchards. U. S. D. A., Farmers' 
Bui. 404. 1910. 

082 



IRRIGATION AND DRY-FARMING 



683 



amount. Irrigation is practiced in all parts of the world 
— in those regions where the rainfall is 50 and 60 inches 
a year, as well as in those regions where it is only 20 inches 
or less. (See Fig. 73.) The need of irrigation is de- 
termined by (1) the time when the rainfall occurs, 
(2) the wav in which it occurs, whether in small or 



s 
1- 
3 
Z 

1 


Ij/ui |n;8|Mflfl|flPfl|rvir|juN[|ji;Lr |/mjc |stn|oCT |nov |occ 


JflN|FtB |MAR|,VR|MflY|jUNt|jlJir |flU6 |StPT | OCT | NOV |D£C 


YUMA 


BUFFALO 


















































































































































































■ 


I 


M 


1 




^ 


1. 


1 


1 


m 


1 


1 


















J 





Fui. 73. — Diagram showing the extent and distribution of rainfall in an 
arid region (Yuma, Arizona), and a humid region (Buffalo, New 
York). 



large quantities, (3) the nature of the soil, (4) the 
air temperature and wind movement, and (5) the nature 
and value of the crops grown. Other factors, such 
as the cost of applying water, methods of tillage, 
and market facilities, have some influence in deter- 
mining the practicability of irrigation. Irrigation is 
usually associated with a low rainfall of 20 or 25 inches 
a year. Using these figures as a measure of the need 
of irrigation throughout the world, it appears that about 
60 per cent of the earth's surface has so low a rainfall that 
irrigation is necessary in order to secure paying yields of 
crops. About 25 per cent of the earth's surface receives 
10 inches or less of rainfall annually. About 30 per cent 
receives between 10 and 20 inches, and about 10 per cent 



684 SOILS: PROPERTIES A.\D MANAGEMENT 

receives between 20 and 30 inches. Every continental 
area has its arid portion where the rainfall drops below 
10 inches. (See Fig. 75.) These sections are usually in 
the interior, but their position depends on the topography 
of the land and the direction of the moisture-laden winds. 
Sometimes, as in the western United States, the coastal 
mountains cause an arid climate in the adjacent interior 
valleys, some of which extend quite out to the ocean as 
in southern California. 



^ 


flN|rc5|fvvi|flFR|Mm |jiiNt |«r |aiig |5tn|ocT|Nov |kc 


JAN 1 FEB 1 hWK |Affl 1 PW |jl)Nt |jULT |«JG |5tn|KT |nOY |0(C 




5m DIEGO 


B0I5E 


25 - 




































20 — 




































15 - 


















_■_ 




1 












1 








1 












1 


1 


II 


_■ 








M 


5 - 








1 


■ 


U 1 


1 I 


1 




1 


1 


1 


■ 


I 


1 




TUCSON 


DENVER 


■4b- 




































20- 




































15 - 


























1 










10 - 


■ 1 


!■ 










1 


■ 


il 




1 


1 


1 


1 


■ 


1 


■ 


5 - 






.A. 




M. 




1 


1 


II 


II 


1 


1 


1 


1 


II 


ll 



Fig. 74.— Four types of rainfall. The diagrams show the distribution 
by months. 



It has been estimated that the total available water 
supply is sufficient to irrigate only one-tenth to one-fifth 
of the proportion of the earth's surface in need of such 
treatment. 



IRRIGATION AND DRY-FARMING 685 

588. Extent of irrigated land. — In 1905, Mead ^ 
estimated the total area of land irrigated at 100,000,000 
acres. Since that date the practice of irrigation has 
been extended rapidly in all parts of the world, and it is 
probable that at the present time the total area of land 
irrigated is at least 200,000,000 acres. In Egypt, in 
Australia, and in India, as well as in the United States, 
large projects for irrigation developments have recently 
been undertaken. In the United States, according to 
the Thirteenth Census, the area of land irrigated increased 
7,500,000 acres between 1899 and 1909. At the latter 
date enterprises for the provision of water were under 
way to cover a total of .31,000,000 acres. 

589. History of irrigation. — The practice of irriga- 
tion is very ancient. The very earliest records of the 
peoples in the valleys of the Nile and Euphrates rivers, 
in Africa and Asia, mention large irrigation works. 
In China and India also the practice is very old. The 
remains of ancient works for irrigation often amaze 
the modern engineer by their size and excellence of con- 
struction, considering the facilities that were available. 
As early as 2084 B.C. an artificial lake fifty miles in cir- 
cumference was constructed in Egypt, communicating 
with the Nile through a canal. The Great Imperial 
Canal in China, connecting the Hoangho River with the 
Yangtze, was 650 miles long and had several lakes in its 
course. In Peru, IMexico, and the southwestern United 
States, there exist remains of very extensive irrigation 
works of great antiquity. In Argentina large irrigation 
canals may still be traced for from four to five hundred 



* Mead, E. Irrigation Engineering and Practice. American 
Cyclopedia of Agriculture, p. 420. New York. 1907. 



686 SOILS: PROPEETIE-S AND MANAGEMENT 

miles. In the Verde River valley in Arizona, remains 
of the cliff dwellings, which were scattered long before the 
advent of the Spanish explorers, are associated with ex- 
tensive irrigation canals showing much skill. The ditches 
and the reservoirs were finished with hard linings of tamped 
or burned clay, and in one instance a main canal was cut 
for a considerable distance in solid rock. Sometimes a 
smaller ditch was sunk in the bottom of a large canal, to 
facilitate the movement of small runs of water. The 
ancient canals in the Salt River valley ^ had a length 
of at least 150 miles and were sufficient to irrigate 25(),(M)() 
acres of land. 

In modern times the great Assouan dam has been built 
on the Nile River, and with the associated reservoirs it 
is designed to control the flow of the river and provide 
water for irrigation. It stands as an example of present- 
day irrigation development and control. 

590. Development of irrigation practice in the United 
States. — In the United States the earliest modern people 
to practice irrigation were the Catholic missionaries in 
southern California. The immediate predecessors of 
the present irrigation systems in the United States were 
built by a colony of one hundred and forty-seven ]\Ior- 
mons who went into the Salt Lake valley in Utah in July, 
1847. The crops of these people were grown with water 
diverted from City Creek, and their community life, to- 
gether with their peculiar situation, led them to work out 
in the succeeding decades the fundamental principles 
of economic and social life as adapted to irrigation farm- 
ing. In the last thirty years the practice of irrigation has 



• Forbes, R. H. Irrigation in Arizona. U. S. D. A., Office 
Exp. Sta., Bui. No. 235, p. 9. 1911. 



TRRIGATION AND DRY-FAUMING 



687 




688 SOILS: PROPERTIES AND MANAGEMENT 

extended rapidly in the western United States. It has 
approximately doubled each ten years since 1S79. 

Irrigation is employed somewhat generally throughout 
the region west of the lOOth meridian, which runs through 
central Nebraska. With the exception of limited areas 
the annual rainfall is less than 25 inches, ami over large 
areas it is less than 15 inches. 

The methods of securing water and applying it to the 
land have grown up gradually out of the experience of 
the people in many communities and under many condi- 
tions. Cooperative effort of some sort is essential to 
provide water for irrigation, and this has led to the use 
of several types of organizations for the purpose. Nat- 
urally, the states concerned have taken a part in the 
matter by passing laws and providing funds to promote 
irrigation practices. Finally, the aid of the Federal 
Government was enlisted. The enterprises for the pro- 
vision of water for irrigation may be divided into seven 
groups,^ chiefly according to their legal status: (1) com- 
mercial enterprises selling water for profit ; (2) partner- 
ships among individual farmers without formal organiza- 
tion ; (3) cooperative enterprises, made up of water 
users ; (4) irrigation districts which are public cori)ora- 
tions ; (5) Carey Act - enterprises, by Federal enact- 
ment authorized August 18, 1894, and made up of 
grants to the arid and semiarid states, these states 
being held responsible for the irrigation of these grants ; 
(6) United States Indian Service enterprises, to provide 
for the construction of irrigation works in Indian reser- 
vations; and (7) the United States Reclamation Serv- 

» Thirteenth U. S. Census, Chapter 14, p. 421. 1910. 
^ Stover, A. P. Irrigation under the Carey Act. U. S. D. A., 
Office Exp. Sta., Ann. Rept. pp. 451-488. 1910. 



IRRIGATION AND DRY-FARMING 689 

ice, established by Federal law June 17, 1902, providing 
for the construction of irrigation works with the re- 
ceipts from the sale of public lands in the arid and semi- 
arid states. 

These several provisions and their successive growth 
in size suggest the necessity of large enterprises and care- 
ful coordination in providing water for irrigation. The 
many attractive features of farming in arid regions under 
irrigation, together with the publicity that the enterprises 
have had, have hastened the growth of irrigation farming 
so that it now plays a very substantial part in the agri- 
cultural business of the country. 

591. Irrigation in humid regions. — In the humid 
states — that is, those in which there is a large normal 
rainfall and in which crops can usually be produced with- 
out artificial addition of water — irrigation has been 
practiced to some extent. • Irrigation is useful (1) where 
the crop has a high value, as for vegetables and small 
fruits near large cities ; (2) where the quality of the crop 
is much affected by unfavorable conditions, as the pro- 
duction of wrapper tobacco in northern Florida and of 
rice in Louisiana ; (3) where the soil is especially sandy ; 
and (4) where the supply of water may be very cheaply 
applied to the land, as in the diversion of streams to adja- 
cent fields, usually meadows. In Great Britain and in 
central and southern Europe, the diversions of streams 
to near-by grass meadows is relatively common. Under 
all these conditions, small irrigation enterprises have 
been developed in different parts of the eastern United 
States. The rainfall under which irrigation is practiced 
in these regions ranges from 30 to more than 60 inches 
annually. The practice of irrigation in humid regions 
is in the nature of an insurance against dry years. The 
2t 



690 SOILS: PROPERTIES AND MANAGEMENT 



probability of the occurrence of these in the eastern 
United States is shown in the following table ' of rainfall 
records for the ten years from 1900 to 1909, inclusive : — 







Number op 


* 






FlPTEEN-DAY 


Number op 




Average 


Periods or 


Days when 


Station 


Annual 


OVER WITH 


Irrigation 




Rainfall 


LESS THAN 


WAS Re- 






1 INCH OK 


quired (o) 






Rain 




Ames, Iowa 


30.39 


23 


190 


Oshkosh, Wisconsin 


29.78 


27 


292 


Vineland, New Jersey . . . 


47.47 


46 


352 


Columbia, South Carolina 


47.55 


62 


568 


Selma, Alabama 


50.75 


60 


724 



(a) No days counted until after a fifteen-day period with less 
than 1 inch of rain. 

The aggregate area of the projects is small and amounts 
to only a few thousand acres. 

592. The Reclamation Service. — The financing of 
irrigation enterprises by the Federal Government through 
the Reclamation Service has been a wonderful stimulus. 
The total number of acres on which ditches have been 
constructed or are in process of construction in this way 
aggregates 3,101,450, in thirty projects distributed through 
seventeen states and invoh'ing a total expenditure of 
hundreds of thousands of dollars. These projects contem- 
plate the impounding of 13,272,490 acre-feet of water. 

1 Williams, M. B. Possibilities and Need of Supplemental 
Irrigation in the Humid Regions. U. S. D. A., Yearbook 1911, 
pp. 309-320. 

Also, Toele, R. P. Irrigation in Humid Regions. American 
Cyclopedia of Agriculture, p. 437. New York, 1905. 



IRRIGATION AND DRY-FARMING 691 

About one-third of this area was irrigated in 1915. Many 
of the dams and canals in\ol\ed are of stupendous size 
and necessitate feats of })old engineering. Often hydro- 
electric power is developed in large amount in the passage 
of the water from the reservoirs to the fields where it is 
to be used to grow crops. 

593. Legal, economic, and social effects of irrigation. — 
The practice of irrigation on an extensive scale has caused 
im])ortant changes in the construction of law ^ relative to 
water and property rights and in commercial and social 
organization. 

Riparian rights in streams and lakes under humid 
conditions, for purposes of domestic use, power, and trans- 
portation, must be modified in an arid country. Here 
values of all real property depend largely on the supply 
of water for purposes of irrigation. The control and use 
of water becomes of the utmost public concern. Conse- 
quently the use of water for the purpose of growing crops 
takes precedence oxer use for all other purposes except 
domestic use. In nearly every country in the world 
where irrigation is extensively practiced, the state or 
the government has assumed ownership or a large measure 
of control over the water in all lakes and streams. The 
necessitv of the use of water for irrigation has conferred 



' Mead, E. Irrigation Institutions. New York, 1903. 

Mead, E. Irrigation Institutions in Different Countries. 
American Cyclopedia of Agriculture, Vol. IV, p. 154. New 
York, 1909. 

Hess, R. H. Further Discussion of American Irrigation 
Policies. American Cyclopedia of Agriculture, Vol. IV, p. 
160. New York, 1909. 

Hess, R. H. Socio-Economic Aspects of Irrigation. Ameri- 
can Cyclopedia of Agriculture, Vol. IV, p. 167. New York, 
1909. 



692 SOILS: PROPERTIES AND MANAGEMENT 

certain privileges, such as the principle of eminent domain, 
in conserving and utilizing water. The provisions differ 
somewhat in detail, Init in general agree in conferring the 
right to use water upon those persons who can first make 
the best use of it for the purpose of growing crops. Other 
rights in the use of water are largely subject to its use for 
irrigation. Further, the tendency is to attach the right 
to the use of water to the title to land, since each has 
value only as it is associated with the other. However, 
in the attachment of water from a particular source to 
any given area of land, many difficult questions may be 
raised which must be decided b}' the larger principle of 
beneficial use. 

A close economic dependence among the people and a 
high degree of social coordination grows out of the practice 
of irrigation farming on a large scale. The fertile nature 
of the soil, the favorable climate, and the cooperation 
necessary to supply water for irrigation, leads to intensive 
methods of farming, to specialization in production, and 
to many cooperative enterprises, not only in agriculture, 
but also in associated industries in the same region. These 
intensive practices and the close personal association 
involved promote a high intellectual and social standard 
in the community. Irrigation has been an efficient school- 
master in the practice and value of cooperation in all sorts 
of enterprises. 

594. Divisions of irrigation. — Two main parts make 
up the practice of irrigation : the first is the provision 
of water, which is essentially an engineering problem ; ^ 
the second is the use of water on the land, which is es- 



' Wilson, H. M. Irrigation Engineering, p. 625. New York, 
1909. 



TERTGATWN AND DRY-FARMING 693 

sentially an afjricultiiral problem. It is important to 
maintain this clear distinction in dealing with the prac- 
tice of irrigation, especially in its larger aspects. The 
two functions are largely exercised by different groups 
of men, and they involve widely different types of knowl- 
edge and skill. The supreme test of an irrigation system 
is efficient use of the water on the land in the production 
of crops. 

595. Sources of water for irrigation. — The practice 
of irrigation is dependent on some adjacent supply of 
water that may be diverted on to the land. It may be 
derived by (1) the diversion of streams flowing from 
well-watered regions; (2) the melting of snow on moun- 
tain areas ; (3) the regulation of the flow of streams by 
storage reservoirs ; and (4) the utilization of underground 
water by means of wells. All these sources may require 
the construction of large and costly works, which are well 
exemplified in the structures built by the United States 
Reclamation Service and by the Egyptian government 
in the Nile valley. Dams hundreds of feet high and 
thousands of feet long, containing millions of cubic yards 
of masonry and concrete, have been constructed for these 
purposes. 

596. Canals. — The conveyance of the water from the 
point of supply to the place where it is to be used necessi- 
tates further difficult engineering problems, which in some 
cases have entailed the construction of large tunnels 
under mountains and the development of large pumping 
and power plants as well as the construction of thousands 
of miles of main and lateral canals. In 1909 the length 
of main irrigation ditches in the United States was 875,911 
miles, and of laterals 38,062 miles. As a rule the water 
is conveyed by gravity flow without pressure. Important 



694 SOILS: PROPERTIES AND MANAGEMENT 

problems presented relate to the prevention of seepaj^e, 
erosion, and evaporation. The loss ^ of water in transit 
from its source to the field has been found to average ()() 
per cent, and to range from 0.25 per cent to as much as 
64 per cent a mile with an average of about 6 per cent. 
The seepage water from canals may result in further loss 
by accumulating in low lands, where the evaporation, 
coupled with the solution of the soluble salts in the soil, 
causes injurious accumulation of alkali in the surface soil, 
and in extreme cases a swampy condition which destroys 
the value of the soil for agricultural purposes. In order 
to prevent seepage many kinds of lining and treatment 
of the walls of canals have been employed. Cement 
lining in different forms, wooden flumes, clay puddling, 
oiling, applications of tar, and silting have been used. 
The need of a lining depends much on the nature of the 
formation through which the ditch passes. Silt is an 
excellent means of checking seepage. Where clear water 
IS carried, the ditch must usually be lined, and the prac- 
tice of lining canals in order to reduce seepage is increas- 
ing rapidly. Sand and gravel permit much seepage and 
are easily eroded. Clay permits little seepage and is not 
easily eroded. The velocity of flow of water in canals 
should not exceed three feet a second. In large canals 
this will not permit a grade of more than six inches in a 
mile ; in very small ditches a grade of from forty to fifty 
feet in a mile may be necessary to ca-use the same velocity 
of flow. A lining that is not subject to erosion, together 



' Teel, R. P. Irrigation and Drainage Investigations. 
U. S. D. A., Office of Exp. Sta., Ann. Rept. 1904, p. 36. Also, 
Mead, E., and Etcheverry, B. A. Lining? of Ditches and Reser- 
voirs to Prevent Seepage Losses. Calif. Agr. E.xp. Sta., Bui. 
No. 188. 1907. 



IRRIGATION AND DRY-FARMING 695 

with a channel that is deep in relation to its width, not 
only reduces seepage, but also, by permitting the rapid 
flow of water, reduces loss by evaporation. 

At the farm on which the water is to be used, it is dis- 
tributed in small field laterals which are carried on the 
higher ground. Precautions against seepage and evapo- 
ration should here be taken. The tendency now is toward 
the distribution of the water to the fields by means 
of underground pipes, with standpipes and valves at 
the points of discharge. The arrangement of the farm 
laterals must of course be determined by the topography 
of the land, since the water flows by gravity. 

597. Preparation of land for irrigation. — The prep- 
aration of the land for irrigation depends on the method 
used to apply the water. Usually marked irregularities 
should be removed by smoothing the surface. Where 
any sort of basin method of irrigation is used, it may also 
be necessary to level the surface. Various types of scrap- 
ers and levelers have been found useful for this operation. 
IVIuch of the arid and semiarid land carries a growth of 
sage brush or other bushy vegetation, and of course 
this must be removed before smoothing operations can 
become effective. 

598. Methods of applying water. — There are four 
general methods ^ of applying water to the soil. These 
are (1) overhead sprays, (2) sub-irrigation, (3) flooding, 
and (4) furrows. 

599. Overhead sprays. — By the overhead spray system 
( Fig. 76) the water is distributed in pipes under a pres- 
sure of forty to sixty pounds and discharged from a series 



• Fortier, S. Methods of Applying Water to Crops. U. S. 
D. A., Yearbook 1909, pp. 293-308. 



696 SOILS: PROPERTIES AND MANAGEMENT 

of nozzles. Several types of nozzles are employed. The 
amount of water that can be applied is relatively small, 
and consequently the method is used chiefly in humid 
regions to supplement a rather high rainfall, in the growth 
of crops of large value. It is used in the growth of truck 
and small fruit crops near the large eastern cities. 

The advantages of the system are : — 

1. The water is conveniently applied at the desired 
point. 2. The system may be used on uneven land and 
without preparation of the surface. 3. There is no 
waste of land by ditches. 4. The application of the 
water is easily controlled by valves and by the movement 
of the pipes. 

The disadvantages of the system are : — 

1. The capacity is limited. 2. The cost is high for 
equipping and maintaining the plant, and for developing 
the pressure requisite to suitably distribute the water from 
the nozzles. 3. There is possibility of injury to crops 
where water is applied on warm, bright days, since the 
water comes into contact with the foliage. 

600. Sub-irrigation. — Sub-irrigation is the distribution 
of water from underground pipes. These are buried in 
the soil and perforated in such a way that the water finds 
an outlet and is distributed by the capillarity of the soil 
and by natural gravity flow. In greenhouses and where 
shallow-rooted annuals are grown, lines of drain tile are 
employed, the water flowing out at the joints. Con- 
tinuous pipes having an open seam or perforations have 
been used. Another method employs a porous cement 
plug which rises a little above the supply pipe. The 
object of the last-named method is to avoid the common 
difficulty from the entrance of roots into the pipes. The 
pipes must have a very slight grade in order to insure a 



IRRIGATION AND DRY-FARMING 697 




flS!d.»^ 



m 



Ju^-' 



!,A 



If" 






I'l, Itr 



Skinner Nozzles. 



//is*^> 



^=^ //?/— 1: »■ 






>f^-/ 



Fig. 76. — Essential features of construction in one method of overhead 
spray irrigation. Water is supplied under pressure from under- 
ground pipes and is distributed from small nozzles (N) along the 
axis of the pipe. Different forms of nozzles are used for different 
purposes (see detail). Gauge (G) shows pressure, (S) is pipe sup- 
port, and (L) is lever for turning the discharge pipe, which is fitted 
with a freely moving sleeve joint. 



698 SOILS: PROPERTIES AND MANAGEMENT 

uniform distribution of water. They operate under 
little or no pressure. The system has a number of ad- 
vantages, but in practice these are usually more than 
offset by its disadvantages. The advantages are : — 

1. The system is permanent. 2. It is economical of 
water. 3. There is no injury to the physical properties 
of the soil. 4. There are no obstructions at the surface. 
5. The deep rooting of crops is encouraged. 6. There is 
very little expense for supervision of the distribution of 
water. 7. The accumulation of soluble salts on the surface 
of the soil by evaporation is reduced. 8. The system may 
sometimes be used as a means of drainage also. 

The disadvantages are : — 

I. There is a strong tendency for the pipes to be clogged 
by the entrance of roots, especially where perennial crops 
are grown. The porous-plug method of discharging water 
is designed to reduce this difficulty. 2. The slow lateral 
capillary diffusion of water in dry soil makes it necessary 
to install the lines of pipe near together, which entails 
heavy expense. 

The method is best adapted to shallow-rooted annual 
crops, and least adapted to orchards. The seepage of 
water from the pipes attracts the growing roots, which 
are likely to enter the pipes, break up into many small 
fibers, and clog the system. 

There are soil conditions under which this methoti is 
especially useful. Where the soil is a porous sand or 
gravel underlaid at a depth of four feet or less by a rather 
impervious stratum, the water may be distributed rapidl\' 
from the pipes so that it accumulates on the hard sub- 
stratum and saturates the soil, the pipes being quickly 
emptied. There is then no tendency for the roots to 
enter the pipes, and the porous nature of the soil permits 



IRRIGATION AND DRY-FARMING 699 

the pipes to be placed several rods apart, thus reducing 
the expense of installation. 

Sub-irrigation sometimes occurs naturally under condi- 
tions similar to those just described, where water is sup- 
plied from springs or by seepage. Where it can be em- 
ployed, sub-irrigation is the ideal method of applying 
water to the soil. 

601. Methods most used in arid regions. — The two 
methods preeminently used to apply water to the soil 
under arid conditions are by furrows and by flooding. 
The land must generally be prepared to some extent for 
either of these methods, by smoothing or leveling the 
surface, throwing up levees, or constructing distribution 
furrows. It is a fortunate fact that the subsoil in arid 
regions is about as fertile as the soil, and therefore grad- 
ing can be practiced with impunity. Both methods have 
a large number of variations in detail to adapt them to 
particular soils, topography, or crops. 

The chief factors determining the choice between flood- 
ing and furrowing are (1) the nature of the crop, (2) the 
character of the soil, (3) the contour of the land, and 
(4) the quantity of water available. 

602. Flooding. — • Flooding is especially employed 
(1) where the crop occupies the entire area, such as in 
grainfields and meadows ; (2) where the soil is of medium 
porosity and does not bake seriously on drying ; (3) where 
the surface is relatively flat ; and (4) where the supply of 
water is relatively large. 

The advantages of this method are : — 

1 . The handling of water is easy. 

2. There is economy in ditches. 

3. The necessity of tearing up the crop is avoided. 

4. The method is especially suited to certain crops 



700 SOILS: PROPERTIES AND MANAGEMENT 

that grow in standing water, such as rice and cran- 
berries. 

Its disadvantages are : — 

1. A large quantity of water is required. 

2. Over irrigation, with consequent seepage and diffi- 
culties from alkali, is likely to occur. 

3. On heavy soil, puddling and checking of the surface 
soil result from lack of tillage. 

4. Some crops are injured by direct contact with water. 

5. The cost of leveling and of construction of levees is 
large. 

There are two main types of flooding. In the first 
the water is turned into level checks or blocks, where 
it stands until it is absorbed by the soil — called commonly 
closed-field flooding. In the second type the water is 
distributed in a moving sheet or a series of small rills, 
from field supply ditches — called open-field flooding. 
This method is used only where there is a moderate slope 
to carry the water. 

In closed-field, or check, flooding, the land is divided 
into blocks, each having a level surface and surrounded 
by a levee. The size of the checks, their shape, and the 
height of the levees is determined by the contour of the 
land. On a slope they may be very irregular. Small 
checks of one to three acres are most successfully irri- 
gated, but areas of twenty or more acres have been flooded 
in one block. A flow of five to seven second-feet of 
water is necessary in order to make the yiethod thoroughly 
successful. One man can irrigate from iive to twenty 
acres a day, depending on the size and form of the checks. 
The levees may be permanent, as is usually the case 
especially in meadows, or they may be thrown up for 
each application of water. The permanent levees may 



IRRIGATION AND DRY-FARMING 



701 



be broad and low so that they will not interfere with 
harvesting. This method of flooding is falling into disuse. 
A phase of check flooding is the basin method of irri- 
gating orchards, in which small, shallow basins are formed 
around each tree and separated from the trunk by a block 




Fig. 77. — Implements used in irrigation practice. {A), scraper for 
making small levees in irrigation furrows; {B), (C), and (D), wood 
and metal topoons used to close irrigation furrows and by means 
of the small openings divide and regulate the flow; {E), canvas 
dam used in flooding from field ditches. The edge of the canvas is 
held down by a shovelful of earth. 



702 SOILS: PROPERTIES AND MANAGEMENT 

of earth to prevent injury to the growing wood. This 
method is used rather extensively throughout the arid 
regions. 

In the open-field, or blind, flooding, the water is sup- 
plied in ditches which are carried across the contours at 
a moderate grade, and at intervals the flow is intercepted 
by a canvas dam or other obstruction and forced to flow 
over the lower bank, from which point it is distributed 
down the slope and over the field in numerous small 
trenches. Any surplus water is collected in a ditch at the 
lower side of the field. In this method of applying water, 
constant attention is required to guide the flow and prevent 
erosion. One man can irrigate from five to ten acres in a 
day. This method is used in irrigating grainfields and 
sloping meadowland and in saturating the soil in prepa- 
ration for a crop. 

603. Furrows. — In the furrow system of irrigation 
the water is led out from the supply ditch on the upper 
side of the field into small, parallel furrows extending 
down or across the slope at a considerable grade. This 
system is used for cultivated field and garden crops, and 
to a large extent in orchards. The rate of flow of water 
in the furrows should not exceed one to two feet per 
second, depending on the nature of the soil. This permits 
a wide range of grade, from 2 to 10 per cent, where the 
head of water is only a fraction of a second-foot in each 
furrow. The flow on a given slope may be regulated by 
the head of water and is determined by the porosity of the 
soil. On heavy soil a small head and a steep grade may be 
employed ; on sandy soil, which washes easily, a low grade 
and a large head of water is used. The length of furrows 
that may be employed depends on the nature of the soil 
and the head of water available. The water is distrib- 



IRRIGATION AND DRY-FARMING 



703 




Fiu. 78. — Plan of irrigated farm showing the methods of irrigating dif- 
ferent crops and the arrangement of the irrigation works for apply- 
ing the water under the different conditions. 



704 SOILS: PROPERTIES AND MANAGEMENT 

uted from the furrows by percolation and by capillary 
movement. Percolation causes the accumulation of 
water under the upper end of the furrows ; capillary move- 
ment distributes the water laterally as well as downward, 



£rr 1 12 




t 
z 

3 
4 


1 1 ^ 


^ 


1 1 




i 


c 


y^ 


^ 


\ 




( \ 


^^^ — 'i 


i^^ 


^ 


^ 




\^ 


^ 
































Fig. 79.^ — Diagrams showing the relative rate of movement of water 
from irrigation furrows into clay loam (left), and sandy loam 
(right), after different periods of time. 

and its rate determines the distance between the furrows. 
The downward ^ movement is much more rapid than the 
lateral movement, and both are very irregular, depending 
on the nature and structure of the soil. Ordinarily the 
furrows are relatively close together, to give greater 
uniformity in distribution. In corn, potatoes, berries, 
garden vegetables, and crops of similar character, a furrow 
is placed in each row, or at least in every other row as is 



» Widtsoe, J. A., and McLaughlin, W. W. The Movement 
of Water in Irrigated Soils. Utah Agr. I^^xp. Sta., Bui. No. 
115. 1912. Also, Loughridge, R. II. Distribution of Water 
in the Soil in Furrow Irrigation. U. S. D. A., Office Exp. Sta., 
Bui. No. 203. 1908. 



IRRIGATION AND DRY-FARMING 



705 



sometimes the case in strawberries, in order to permit 
harvesting. 

In orchard culture two or more furrows are placed 
between each two rows. Often for young trees a furrow 
is placed on either side at a distance of about two feet, 
this distance being increased as the trees increase in size. 
The furrows are temporary and are usually renewed 
after each application of Avater, as the establishment of a 
soil mulch is necessary in order to prevent excessive loss 
of water by evaporation. 

604. Size and form of furrows. — In shape the fur- 
rows should be relati\ely narrow and deep. Water is 
conserved by this form in three ways : (1) it flows more 
freely, both in the furrow and into the soil ; (2) less surface 
is exposed to evaporation ; and (3) the surface mulch is 
more easily maintained. (See Fig. 80.) Under arid con- 
ditions a deep mulch ^ of six to eight inches is most 



jrr z t 





1 


z 




1 

2 

z 


\ 




CD 


^ 




• MULCH 


4yr. 


\^' 




( 


Xo 


Y^ 


1 











( 


-^ 




-^ 


V 















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2 
3 


1 1 1 1 1 


" .■ MUL 


"I 


y^ 


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T' 






^~^ 



























Fi(j. 80. — Diagram showing the relative advance of water into the soil 
from a deep (left) and a shallow (right) irrigation furrow. Note 
the relative extent of surface soil wet in the two cases. A deep 
mulch and deep irrigation furrows aid in the conservation of 
moisture. 



1 Fortier, S. Evaporation Losses in Irrigation and Water 
Requirements of Crops. U. S. D. A., Office Exp. Sta., Bui. No. 
177. 1907. 
2z 



706 SOILS: PROPERTIES AND MANAGEMENT 

efficient, and the bottom of the furrow should extend 
well below its base. This will allow the water to diffuse 
laterally rapidly, and the deep dry mulch reduces the 
extent to which the surface becomes moist, thereby con- 
serving moisture and reducing the accumulation of alkali 
at the surface. 

The application of water to the soil in irrigation must 
be guided by the principles elucidated in the discussion of 
the physical properties of the soil, and its relation to 
moisture and its control. 

605. Units of measurement. — The measurement of 
water in irrigation j)racti('c involves the use of unlets of 
volume and pressure. By the head is understood the 
volume of water supplied in the unit of time. The flow 
of water in canals is usually stated in units of flow per 
unit of time, that is, the number of cubic feet per second, 
called the second-foot. Frequently the term second-foot 
is applied to the volume of water that would result from 
a flow of that rate throughout the season. A smaller 
unit is the miner's inch, a term derived from mining 
practice, which refers to the quantity of water that will 
flow out of an orifice one inch square under a constant 
pressure which varies in different states from a four to 
an eight inch head above the top of the orifice. Like the 
second-foot, the flow is frequently rated by the season. 
The pressure is proportional to the depth, or head. It is 
commonly stated in pounds per square inch. A column 
of water ten feet in height exerts a pressure of approxi- 
mately 4.34 pounds to a square inch. 

In the field, water is commonly measured in terms of 
depth over an acre. An acre-foot is the quantity of water 
that will cover an acre one foot in depth. An acre-inch is 
one-twelfth of an acre-foot. These are very convenient 



IRRIGATION AND DRY-FARMING 



707 



terms because of their definiteness and relation to the 
common method of stating rainfall. Usually an inch or a 
foot of water refers to that depth over an acre. 

Various mechanisms are employed for measuring ^ 
water in irrigation practice. The commonest of these 
are the weir and the flume. (See Fig. 81.) The weir is 







%W^'"<-:. 



Fig. 81. — Plank measuring box and a Cippoletti weir used in determin- 
ing the flow of irrigation water. 



a simple device to give the stream a definite cross section 
and to aid in the measurement of the depth, and there- 
fore the volume of flow. It is usually a knife-edged notch, 
of a standard shape calibrated to a grade stake a short 
distance up stream from which the depth of water and 
its velocity are rated. The measuring box, frequently 
termed a module, is a box for measuring the flow of water 
from an orifice under fixed conditions. The Staldate 
module, developed in Italy, is most generally adopted for 
the purpose. Small streams are divided by a knife-edge 



' Carpenter, L. C. The Measurement and Division of Water. 
Colorado Agr. Exp. Sta., Bui. No. 150, 4th ed. 1911. 



708 SOILS: PROPERTIES AND MANAGEMENT 



diverter inserted into the current, which diverts a definite 
portion of the stream. This is called a divider. 

606. Amount of water to apply. — The amount of 
water to apply to the soil at any one time depends on 
(1) the nature and condition of the soil, (2) the supply of 
water, ('A) the crop, and (4) the season. In the main, 
enough water should be applied to capillarily saturate 
the soil to a depth of one foot and to increase the soil 
moisture to a dejjth of three feet. A fairly dry, fine- 
textured soil will effectively take the largest irrigation. 
Some crops are more sensitive to water at one period of 
growth than at another. Potatoes should mature in a 
rather dry soil. The application of water at a single 
irrigation should ordinarily be from four to eight inches. 
In very hot weather it may be reduced to two or three 
inches. In late fall or early spring, when the soil is 
unoccupied, the application may be relatively larger 
provided the soil is dry. 

Excessive irrigation is to be avoided. While the total 
yield increases with increase in the application of water 
up to the maximum point, the unit production decreases.^ 
The following brief table, calculated by Widtsoe from 
actual yields of wheat, illustrates this point : — 





Thirty Acre-inches of Water spread over 




1 acre 


2 acres 


3 acres 


4 acres 


6 acres 


Grain (bushels) 
Straw (pounds) 


47.51 
4532 


91.42 
2908 


130.59 
10256 


166.16 
13204 


226.16 
17916 



1 Widtsoe, J. A. The Production of Dry Matter with Dif- 
ferent Quantities of Irrigation Water. Utah Agr. Exp. Sta., 
Bui. No. 116. 1912. 



IRRIGATION AND DRY-FARMING 709 

Small applications of water are relatively most efficient. 
Up to the limit where injury results, the more concentrated 
the soil solution, the larger is the yield of crop. 

607. Time to apply water. — The best time to apply 
water depends to a large extent on the nature and habits 
of the crop. Ordinarily the soil should be thoroughly 
moistened at the time of planting, in which case the 
application will have been made before fitting the ground. 
For sugar beets and other crops planted in rows, it is 
permissible to irrigate immediately after seeding. The 
formation of a crust is to be avoided. After planting, 
water may be applied at intervals of two or four weeks, 
or when the soil has reached the stage of dryness at which 
sluggish capillary movement occurs. The experienced 
irrigator becomes very proficient in recognizing this con- 
dition. For grain and forage crops, the soil should be well 
moistened when the crop approaches maturity. For al- 
falfa, irrigation may be either shortly before or just after 
harvest with good results. For root crops a relatively 
dry condition of the soil at maturity is preferred. The 
same is true for trees, and the large application of water 
late in the growing season is especially to be avoided 
because the new wood growth is likel}^ to be winter- 
killed. Irrigation in spring, especially at blossoming time, 
is to be avoided because it interferes with the setting of 
fruit. One or two thorough irrigations in a season are 
usually sufficient for the growth of trees. Small fruits 
should have plenty of water at the maturity of the crop. 

Where water is available in late fall and in winter, it 
may be applied to the soil and stored there for use during 
the following season. Investigations at the Utah ^ station 

1 Widtsoe, J. A. The Storage of Winter Precipitation in 
Soils. Utah Agr. Exp. Sta., Bui. No. 104. 1908. 



710 SOILS: PROPERTIES AND MANAGEMENT 

have shown that moisture may be effectively stored in the 
soil to a depth of more than eight feet and be reacHly used 
by crops the next season. The total amount of water to 
be ap})lied depends on many things. The following factors 
affect the duty of water: (1) character of the crop; 
(2) climate ; (3) texture and structure of the soil ; (4) depth 
of the soil ; (5) fertility of the soil, including the total 
amount of soluble material ; (G) kind of tillage practiced ; 
(7) thickness of ])lanting ; (8) season when the crop grows ; 
(9) frequency and method of applying water ; (10) amount 
and time of applying water. A fertile soil and a large 
and rapid growth of the crop go with economy of water. 
Many of the above factors, such as thickness of planting, 
tillage practice, and manner of using water, determine the 
loss from the soil that has no direct relation to the crop. 

The total amount of water to be applied ^ in irrigation 
should range from five to twenty inches, with the tendency 
toward the lower figure. This means a duty of 280 to 
75 acres a second-foot for a season of sixty days. From 
one to four applications of water are usually made. The 
larger the plant and the deeper the root system, the larger 
the individual application of water may be, and the fewer 
the number of applications. 

608. Conservation of moisture after irrigation. — The 
conservation of moisture applied i)y irrigation should be 
provided for whenever practicable. Crops planted in 
rows should be cultivated as soon as the soil is dry enough 
not to puddle. As suggested abo^•e, when the furrow 
method is em])loyed the furrows should be deep, so that 
only a small part of the surface soil will be wet. Coupled 



1 Widtsoe, J. A. Principles of Irrigation Practice, Chapter 
XVII. New York. 1914. 



IRRIGATION AND DRY-FARMING 711 

with this, a mulch of dry soil from four to eight inches 
deep should be maintained. This is a protection against 
too high a temperature in moist soil unprotected by shade, 
as well as against loss of moisture. The surface of the 
soil should be kept as nearly level as possible. 

Crops that are not planted in rows, such as grain, may 
be cultivated with a fine-tooth harrow until they reach a 
height of from several inches to a foot, at which stage 
evaporation from the soil is largely prevented by the 
shading of vegetation. If it is to be successful this culti- 
vation must begin as soon as the seedlings appear above 
the surface, in order that the roots may be forced deep 
into the soil. Then the top may be much twisted with 
but little injury to the plant, and that injury appears to 
be more than counterbalanced by the tillering of the plant. 
By prompt and thorough tillage following~irrigation, very 
much may be done not only to conserve soil moisture but 
also to prevent the accumulation of alkali at the surface 
by evaporation. 

609. Sewage irrigation. — A phase of the general prac- 
tice of irrigation is the application of sewage ^ to the land 
for purposes of crop production. This supplies plant-food 
as well as water. The food content, however, is relatively 
small, being about two parts in one thousand, of which 
one-half is organic and one-half is inorganic material. 
In European countries sewage irrigation is extensively 
employed near cities, but in the United States the practice 
.has not been largely followed. The city of Boston has 
carried out extensive experiments, and the city of Los 

' Rafter, G. W., and Baker, M. N. Sewage Disposal in the 
United States. New York. 1904. Also, Rafter, G. W. Sew- 
age Irrigation. U. S. Geol. Survey, Water-Supply and Irrigation 
Papers, Nos. 3 and 22. 1897 and 1899. 



712 tiOILS: PROPERTIES AND MANAGEMENT 

Angeles has a large farm irrigated with sewage water. 
The same general principles prevail in the use of water 
as in normal irrigation practice, except that the soil may 
become clogged and foul from the accumulation of solid 
material, especially where the idea of disposal over- 
shadows that of efficient use. This practice is used 
chiefly for the production of hay and forage. 

DRY-FARMING 

The water supply for irrigation is sufficient for only a 
small part of the earth's surface which needs such treat- 
ment. The remainder of this vast area of land having a 
deficient rainfall must be utilized, if at all, by the most 
scrupulous and careful conservation and use of the natural 
rainfall. The growth of crops without irrigation under 
such conditions is termed dry-farming.' It is merely an 
intensified form of the methods which are recognized 
as good practice to conserve moisture in more humid 
regions. 

Dry-farming is based on the principle that the production 
of dry matter in crops requires only a small part of the 
water which may be used in one way or another in its 
growth, and that a large part of that water is lost by sur- 

1 Widtsoe, J. A. Dry Farming. New York. 1910. (Appendix 
includes a large list of references on dry land farming.) 

MaeDonald, Wm. Dry Farming. New York. 1910. 

Campbell, H. W. Soil Culture Manual. Lincoln, Nebraska. 
1907. 

Chileott, E. C. Dry Farming in the Great Plains Area. " 
U. S. D. A., Yearbook, pp. 451-4()8. 1907. 

Lriggs, L. J., and Shantz, H. L. The Water Requirement 
of Plants. Investigations in the Great Plains in 1910 and 1911. 
U. S. D. A., Bur. Plant Ind., Bui. 284. 1913. Also, the Water 
Requirements of Plants. A review of literature. U. S. D. A., 
Bur. Plant Ind., Bui. 285. 1913. 



IRRIGATION AND DRY-FARMING 713 

face flow, by seepage, and especially by evaporation, 
without performing any useful service to the plant. 

610. Practices in dry-farming. — The practice of dry- 
farming may be divided into three groups : (1) the main- 
tenance of such a condition of the soil at all seasons of 
the year as will insure the complete absorption of the 
rain- and snow-fall ; (2) the conservation of the stored 
moisture by appropriate methods of tillage ; (3) the selec- 
tion of drought-resistant crops and of rotations adapted 
to the small use of water. 

611. Storage of water in the soil. — In different regions 
the rainfall occurs at different seasons. A loose, open 
condition of the surface soil should be maintained during 
that period. This may require deep plowing, and if the 
subsoil is compact it may include subsoiling. Where 
the precipitation comes as snow, the surface should be 
rough so as to prevent drifting, in order that the resulting 
water may be uniformly absorbed by the soil. Fall 
plowing is an important factor where much of the pre- 
cipitation comes in winter and tlie soil is compact. 
Another reason for the maintenance of a ridged surface 
is to reduce erosion by the high winds which frequently 
occur in winter in dry-farming regions and which cause 
the serious removal of the soil. The roughened surface 
impedes the wind movement, and the moist soil at the 
crest of the ridges resists erosion. 

612. Conservation of moisture. — The conservation of 
the moisture in the soil involves two things - — an increase 
in the capillary capacity of the soil, and the prevention of 
evaporation. Where the rainfall is low, the deep subsoil 
is usually very dry. The rainfall penetrates to a limited 
distance from the surface. Having loosened the subsoil 
so that the rainfall is absorbed, the next step is to compact 



714 SOILS: PROPERTIES AND MANAGEMENT 

the substratum as much as possn)le by tillage in order to 
increase its capillary capacity. The need of this treat- 
ment, of course, depends on the nature of the soil, and 
is not always the most fa^■orable. It is undesirable that 
this packing should extend to the surface. Following the 
plow, the land is frequently worked down with a subsur- 
face packer, an implement of considerable weight, made 
up of openwork rims that press the soil together and at 
the same time leave a mulch on the surface. By acting 
on the lower part of the furrow instead of on the surface, 
the packer brings it into closer contact with the subsoil 
and thereby establishes better capillary connection. 

After thorough packing of the main part of the furrow, 
a dust mulch is maintained on the surface. This should 
be of medium depth in the season when rains are likely 
to occur, and of somewhat greater depth during the 
dry period. Two or three inches is usually a sufficient 
depth. 

Various applications of the principle of mulching ma>- be 
employed. Land may be disked before plowing in fall or 
spring, to hold moisture until the plowing can be done. 
As soon as a crop is removed, the land should be plowed 
or fitted and worked down to a good mulched surface. 
Land should not be allowed to stand" un worked for any 
considerable time after harvest. All rowed crops should 
be kept thoroughly mulched. INIuch ma>- be done to 
conserve water in grain and hayfields by tillage. The 
same principles apply to the ])ractices that are used on 
irrigated land. Special revolving toothed implements 
have been devised to loosen up the surface soil under 
such conditions. 

613. Alternate cropping. — Where the rainfall is too 
light in a single season to permit the production of a profit- 



IRRIGATION AND DRY-FARMING 715 

able crop, it is sometimes the practice to collect and store 
the rainfall of two seasons in the soil. This is the system 
of alternate-year cropping. In the intervening year the 
soil is carefully fallowed and mulched, to hold the stored 
moisture. That such long-time storage of available 
moisture is possible has been clearly demonstrated ' under 
dry-farming conditions, and also in the study of irrigation 
problems. An arid or a semiarid climate is especially 
favorable for the formation and maintenance of an effi- 
cient dust mulch, and the occurrence of dry earth in the 
lower subsoil permits moisture to be stored and retained in 
large quantities within reach of the roots of crops. It is 
believed by some persons that the practice of fallowing 
in alternate years is very destructive of organic matter 
in the soil, and that it may be better to grow a green- 
manure crop in that period to be turned under. It is 
questionable whether the loss of water may not be a 
serious objection to this. 

614. Drought-resistant crops. — For gro\\i;h under dry- 
farming conditions, crops are preferred which have a low 
moisture requirement, which are not seriously affected 
by severe drying, and which have a fairly deep root system. 
The sorghums come in the first class and also fulfill the 
second requirement. Corn is fairly satisfactory. Wheat, 
barley, and alfalfa are favorite dry-farm crops. Drought- 
resistant varieties of these crops are being sought. A 
rotation is desirable which exposes the soil as little as 
possible to evaporation, and permits continuous mulch- 
ing with the minimum of plowing. 

' Atkinson, A., Buekman, H. O., and Gieseker, L. F. Dry- 
Farm Moisture Studies. Montana Agr. Exp. Sta., Bui. 87. 
1911. Also Burr, W. W. Storing Moisture in the Soil. Ne- 
braska Agr. Exp. Sta., Bui. No. 114. 1910. 



716 SOILS: PROPEIiTIES AND MANAGEMENT 

615. Soils associated with dry-farming. — Dry-farming 
is often closely associated with irrigation, being practiced 
on the heavier soils where the water-storage capacity is 
large and where the practice of irrigation is most difficult. 
Successful dry-farming requires an annual rainfall of at 
least fifteen inches, and twenty inches is much safer as a 
basis for the practice. A general principle to be observed 
in dry-farming is that the shorter the soil moisture supply, 
the lighter should be the rate of seeding. Wheat, for 
example, may be seeded at the rate of only twenty pounds 




Fig. 82. — Areas of western United States where dry-land farming is or 
may be practiced. 



IRRIGATION AND DRY-FARMING 717 

to the acre. The crop will stool out strongly and adjust 
itself to the moisture supply. Under dry-land and irri- 
gation farming, crops as a rule root much deeper than in 
humid soils. 

616. Extent of dry-farming. — In the United States 
many thousands of acres in the Great Plains region, in 
the semiarid northwestern valleys, and in the Pacific 
Coast States, are now being cropped under systems of 
dry-farming (see Fig. 82). Further, the practice is be- 
ginning to be followed somewhat more definitely in all 
parts of the world where similar conditions prevail. The 
large open areas of land and the dry climate in such 
regions have encouraged the employment of larger power 
equipment in planting and harvesting the crops, especially 
wheat. In parts of California machines are used which 
cut, thresh, and sack the grain in one operation. 

The study of the principles on which dry-farming is 
based, together with the extension of their practice, 
may be expected to bring large areas of land, now sub- 
stantially worthless, to a measurable degree of productive- 
ness. The tendency in the practice of both dry-farming 
and irrigation is toward the more efficient use of water 
for purposes of crop production, and to approach the 
actual requirements of the plant in the utilization of water. 
In both cases the fundamental principles in the storage, 
conservation, and use of water by plants must be observed, 
as well as care regarding the application of these prin- 
ciples according to the soil, the crop, and the nature of the 
water supply. 



CHAPTER XXXI 

THE SOIL SURVEY 

The function of the soil survey is to investigate the 
nature and occurrence of soils in the field. The soils are 
classified into areas haN'infj approximately the same crop 
relations and tillao;e properties. The location of the areas 
of each kind of soil is represented on charts or maps, and 
their character and chief economic and agricultural rela- 
tions are described in printed reports. 

617. The classification ' of soils by survey. — The 
occurrence of differences in the tillage and manurial re- 

* Klassifieation, Nomenclature, und Kartierung der Boden- 
arten. 

Verhandlungen der zweiten internationalen Agrogeologenkon- 
ferenz. (Proceedings of the Second International Agro-geological 
Conference, Stockholm, Chapter V, pp. 223-298. (Seven papers.) 
1911. 

Report on Soil Classification. Proc. Amer. See. Agron., Vol. 
6, No. 6, pp. 284-288. 1914. 

Fippin, E. O. The Practical Classification of Soils. Proc. 
Amer. Soc. Agron., Vol. 3, pp. 70-88. 1911. 

Marbut, C. F. Soils of the United States. U. S. D. A., 
Bur. Soils, Bui. 96, pp. 7-lG. 1913. 

Coffey, G. N. A Studv of the Soils of the United States. 
U. S. D. A., Bur. Soils, Bui. 8.">, p. 114. 1912. 

Hall, A. D., and Russell, E. J. Soil Surveys and Soil Analy- 
sis. Jour. Agr. Sci., Vol. 4, Part 2. 1911. 

Tularkov, N. The Genetic Classification of Soils. Jour. 
Agr. Sci., Vol. 3, pp. 80-85. 1909. 

Stevenson, W. H., Christie, G. I., and Willco.x, O! W. The 

718 



THE SOIL SURVEY 719 

quirements of soils, their crop relations, and their agri- 
cultural value make necessary the determination of the 
properties of the soil that are chiefly responsible for those 
differences, and their arrangement into an orderly scheme 
of classification. The aim is to divide the land into 
areas of approximately the same general character. This 
volume is largely an exposition of those properties of soils 
that make differences in their crop relations and manage- 
ment. It is evident that differences are numerous and 
varied, and that some have greater significance than 
others. 

Soils may be classified from many different points of 
view. The basis may be purely geological, purely physical, 
or almost entirely chemical. Any one of these alone is 
likely to be inadequate for the purposes of the agriculturist. 
The viewpoint of the agricultural soil survey should be 
such as to secure unity in the crop relations of each distinct 
area of soil recognized. 

The system of classification in use must employ as a 
basis some combination of the groups of properties enu- 
merated above. The combination selected has differed 
in different parts of the world, depending on the training 

Principal Soil Areas of Iowa. Iowa Agr., Exp. Sta., Bui. 82. 
1905. 

Mooers, G. A. The Soils of Tennessee. Tennessee Agr. 
Exp. Sta., Bui. 78. 1906. 

Sherman, C. W. The Indiana Soil Survey. Dept. Geol. 
and Natural Resources, 32d Ann. Rept., pp. 17^7. 1907. 

Hopkins, C. G., and Pettlt, J. IT. The FertiHty of Illinois 
Soils. IHinois Agr. Exp. Sta., Bui. 123. 1908. 

Hall, A. D., and Russell, E. J. Report on the Agriculture 
and Soils of Kent, Surrey, and Essex. Dept. Bd. Agr. and Fish- 
eries. London. 1911. 

Kiimmel, A. B. Soil Surveys as Related to Geology. N. J. 
Bd. Agr., 36th Ann. Rept., pp. 162-169. 1908. 



720 SOILS: PROPERTIES AND MANAGEMENT 

of the person by whom the survey was proposed, and the 
kinds of soils and crops with which he dealt. Some 
persons have used the vegetation,^ especially the native 
vegetation, as a means of classifying soils. Where this 
is present it is an excellent means of identifying differences, 
and pioneers as well as others have always made use of 
the vegetation growing on a soil to detect variation in 
its cropping capacities. Unfortunately the vegetation, 
whether native or introduced, being a result of natural 
causes, affords information regarding the properties of a 
soil only when the correlation has been worked out. 
l^\irther, the native vegetation is now seldom present in 
well-settled areas, so that it is inadequate as a general 
means of classification, though very useful for some 
purposes of comparison. 

618. Factors employed in classification. — In classify- 
ing soils, four primary and two secondary factors are 
employed. The former group deals entirely with the 
soil itself ; the latter group deals with the climate or the 
situation in which the soil is placed. The situation exerts 
an influence on the crop value and on the properties of the 
soil. The factors, beginning with those of the smallest 
range of occurrence, are as follows : (1) texture, (2) special 
properties, chiefly chemical, (3) kind of material from 
which the soil was formed, (4) agency of formation, 
(5) humidity and precipitation, and (6) normal and 
mean temperature. 

The soil type is the unit of .classification, and may be 
defined as an area of soil that is essentially alike in all the 
above characters. 



1 Hilgard, E. W. Soils, Chapters XXIV, XXV, and XXVI. 
New York. 1906. 



THE SOIL SURVEY 



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722 SOILS: PROPERTIES AND MANAGEMENT 

619. Texture — the soil class. — Of all the properties 
of the soil, the one which is most apparent and which 
exerts the most direct influence on the plant is the tex- 
ture, or fineness of division, of the soil particles. Is it a 
clay, a silt, a sand, a gravel, or some combination of these ? 
Is it stony, or is it free from stone? The texture is the 
first property made use of in classifying soil. This divi- 
sion based on texture is called the soil class. It is a purely 
physical division, and does not recognize any chemical 
or other differences in the soil except as such differences 
may occur between coarse and fine materials. 

620. Special properties — the soil series. — Soils of 
different texture may be alike in other properties. They 
may be all red, all black, or all yellow. They may be 
well drained or poorly drained. Such a group of soils of 
different texture but alike in all other pr()j)erties consti- 
tutes a soil series. The properties by which the soil 
series is recognized are (1) color, which is predominant 
in tlie separation, (2) content of organic matter, (3) natural 
drainage, (-4) content of lime carbonate, (5) ultimate 
chemical composition, and (6) arrangement of the soil in 
the section. Any one or a combination of these properties 
may identify an area of soils. Such an area would con- 
stitute a soil series. These properties permit the recog- 
nition of chemical differences quite as much as physical 
differences of the soil in mass. 

If it were possible clearly to identify all the properties 
that may be recognized in the series and class divisions, 
there would be no need of employing other factors in the 
classification. Such a clear identification, however, is 
only partially ])()ssii)le, and is further lunited by the 
conditions under which the soil survey must be carried 
out in the field. Many of these properties are of such 



THE SOIL SURVEY 723 

an intimate nature that they cannot be recognized by 
inspection. However, they are correlated with the origin 
and mode of formation of the soil, and therefore the use 
of those factors in the classification is justified as an aid 
to rapid and accurate field identification. 

621. Source of material — the soil group. — The soils 
of a region may be similar in many properties because 
they have been derived from the same kind of rock. They 
may be similar also because they have been derived from 
the same mLvture of different rock materials. As a result 
of the many kinds of rock and the different proportions in 
which they may be mingled, many groups of soil series 
may be recognized. Some of the commoner groups of 
rocks identified with these differences are acid and basic 
crystalline rocks, shales, sandstone, and limestone. 

622. Agency of formation — the soil province. — The 
way in which a rock formation has been broken down and 
the residue brought to its new resting place affects both 
the chemical and the physical nature of the resultant soil. 
The six groups of forces that have been predominant 
in the formation of soils are : (1) weathering, or the 
decay and disintegration of rocks in place, forming a 
residual soil ; (2) biological processes, which form organic 
matter and give rise to cumulose soils ; (3) water in 
streams, lakes, and oceans, which reduces, transports, 
and sorts soil-forming materials, and which imparts to its 
deposits a distinctly stratified arrangement ; (4) atmos- 
phere, especially as regards wind, which exerts an abra- 
sive and sorting action similar to that of water but with 
a very much smaller range in the texture of the strata 
formed, and with a type of stratification also distinct 
from that formed by water ; (5) glaciation, or the action 
of continental masses of ice, the deposits from which are 



724 SOILS: PROPERTIES AND MANAGEMENT 

exceedingly heterogeneous in nature and are without 
sorting or stratification except as the action of wind and 
water may have combined with the action of the ice ; 
(6) gravity, or the slow creep of material on slopes, which 
is a minor agency of soil formation (see Chapter II). 

623. Climate. — Soils owe their origin to the operation 
of one or more of the forces named above. Usually some 
one of these agencies is predominant and gives specific 
character to the soil. The elements of climate have been 
used in the practical classification of soils to only a small 
degree, since the inherent properties of the material in 
these divisions are usually distinct enough to make sepa- 
ration easy. The excessive accumulation of the soluble 
salts known as alkali is associated with a low rainfall, 
and other chemical and physical properties are correlated 
with aridity. Three main divisions in humidity and pre- 
cipitation may readily be made, namely, (1) humid, 
(2) semiarid, (3) arid. The exact precipitation limits of 
these divisions depend on the temperature relations and 
the time and manner of occurrence of the precipitation. 

In a world system of soil classification the temperature 
relations of the soil would be recognized, but this division 
is seldom important in any single country. 

624. The practical classification of soils in the United 
States. — As practiced in the United States, the classi- 
fication of soils ^ has disregarded the climatic factor and 
has usually combined the kind of rock and the agencies 
of formation as a single basis of separation of soils, dt^sig- 
nating the division resulting therefrom as a soil province. 
In some areas one element of formation is dominant and 

1 Marbut, C. F., Bennett, H. TI., Lapham, J. E., and Lap- 
ham, M. H. Soils of the United States. U. S. D. A., Bur. 
Soils, Bui. 96, p. 891. 1913. 



THE SOIL SURVEY 725 

in other areas another element is dominant. To this 
extent the classification deviates from the ideal system 
outlined above. 

625. The soil type and series. How characterized and 
named. — The two predominant divisions of soil are the 
soil tyj)e and the soil series. The soil type is the unit 
of field study and classification, and corresponds to a 
species of plant or animal in biological classification. It 
includes all those areas of soil that are essentially alike 
in all properties — texture, color, chemical nature, struc- 
tural properties, source of material, and mode of forma- 
tion. In other words, soils of the same type are as nearly 
alike as field identification will admit. The soil series is 
a group of types differing only in the texture of the differ- 
ent members. This may be said to correspond to the 
genera in biological classification. 

A name is given to each series of soil for purposes of 
easy identification, and to this name the class designation 
is added, thereby fixing the identity of the type. For 
example, the ]Miami series includes certain light-colored, 
timbered, glacial soils of the East Central States. The 
Hagarstown series includes certain light brown to reddish 
residual limestone soils, found in the blue-grass region of 
Kentucky and adjacent states. The Norfolk series in- 
cludes lemon yellow, marine-deposited soils of the coastal 
plain of the Atlantic and Gulf regions. Clay loam would 
refer to a particular texture of any of these series, as the 
Miami clay loam, for example, thus completing the type 
name of a soil, which is made up of the series name and 
the class designation. 

The common practice is to select for the series desig- 
nation some geographical name in the region where the 
soil is first identified or is best developed. The word 



726 SOILS: piiOPEirriEs Ayn management 

Miami is taken from the iNIiami River in southwestern 
Ohio, where the ]Miami series was first recognized. 

Tliis system of a proper generic name and a descriptive 
class name is most widely used in the United States to 
identify the soil type. It gives a specific identity of the 
soil in its situation and in all its properties. 

Hopkins ^ has proposed and used the Dewey Library 
System of numerical naming of soils, by which each prop- 
erty is given a fixed series of numbers and the identifica- 
tion number is obtained by combining the numbers that 
represent its properties. \Miole numbers are assigned to 
important and definite soil types, and decimals are used 
for related types possessing some distinct variations. 
F'or example, 451.2 represents a glacial soil made up of 
brown loam on silt. While the numbering system of 
designation is admirable in many ways, it does not lend 
itself to the same practical use that is possible with a 
proper descriptive name. 

626. The equipment for survey work. — The most 
important part of the equipment for soil survey work is 
the field man. He should be a keen and careful observer, 
and he should have had broad training for his work. He 
should be acquainted with the technic of soils in the labora- 
tory and in the field. He should be familiar with the 
chief physical and chemical processes and material in- 
volved in soil formation. He should have an inider- 
standing of that phase of geology known as physiography. 
On the agricultural side, he should be acquainted with 
plants and the methods of growing the more important 
crops. He should know tillage practice, and should be 



1 Hopkins, C. G., and Pettit, J. H. The Fertility of Illinois 
Soils. Illinois Agr. Exp. Sta., Bui. 123, p. 252. 190S. 



THE SOIL SURVEY 121 

able to distinguish between the properties of the soil that 
are native and permanent and those that may be induced 
by the method of handling. There is very little knowl- 
edge of natural phenomena that will not be found useful 
to the field man in classifying soils, because he uses all 
sorts of observations in making and checking his divisions 
in soils. Tn brief, he should have a good training in the 
fundamental technic of geology, chemistry, and agricul- 
ture. 

In the way of physical equipment the field man should 
have a good map of the region, on a scale of one inch to 
a mile or larger. The field work should be done on at 
least as large a scale as the finished map, as this increases 
the degree of accuracy. The map should show the roads, 
streams, and towns of the region, and in addition the 
topography, location of houses, and other natural and 
cultural features which are useful in placing boundaries 
of soil. Where a satisfactory map is not available the 
field man must make such a map ^ during the progress of 
the soil survey. For this purpose a Gannett plane table, 
a sight alidade, and some method of measuring distance — 
preferably an odometer, such as is used for counting the 
revolutions of a buggy wheel — are necessary. Cloth- 
back drawing paper is generally used. 

Where a suitable base map is already available, a set 
of pencils of dift'erent colors for representing each type of 
soil on the map as it is recognized is essential. A horse 
and buggy is the usual method of conveyance. For ex- 
amining the soil a soil auger is used (see Fig. 83). This 
consists of a one-and-one-half-inch wood auger attached to 
a half-inch pipe rod with a T handle, making a total length 

1 Instruction to Field Parties. U. S. D. A., Bur. Soils. 1914. 



728 SOILS: PROPERTIES AND MANAGEMENT 



^ 



of about thirty-eight inches. By the use of additional 
sections the length may be increased. The end of the 
auger may be modified by cutting off 
the screw and the cutting jaws, to 
better adapt it to the work in soil. 
Generally a bottle of muriatic acid 
for detecting carbonates, and strips 
of sensitive litmus paper of red and 
blue for testing for soil acidity, are 
useful adjuncts to the ecjuipment. In 
arid regions where important quanti- 
ties of alkali are met with, the field 
man should be supplied with a modi- 
fied Wheatstone bridge and chemical 
equipment necessary for the detection 
and measurement of the important 
salt constituents.^ A geologist's ham- 
mer for examining soil and rock should 
be added, together with such other 
minor equipment as may increase the 
convenience and efficiency of the work. 
A substantial field book should be 
provided, for notes on the character 
of soil types and other observations 
and data, and for records of borings 
and samples. The notes should be 
carefully classified. INIuslin bags of 
about one quart capacity should be used for collecting 
and shipping the samples to the laboratory for mechani- 
cal analysis. Where the natural field structure and 

1 Davis, R. 0. E., and Bryan, H. The Electrical Bridge 
for the Determination of Soluble Salts in Soils. U. S. D. A., 
Bur. Soils, Bui. (U. 1910. 



Fig. 83. — Auger used 
in the examination 
of soils. (A), 
handle ; (B) , joint ; 
(C) , worm with 
modified cutting 
edge. 



THE SOIL SURVEY 729 

moisture conditions of the sample are to be preserved, 
wide-mouth, sealed-top, metal or glass containers should 
be used. Aluminum cans are usually most suitable, as 
they are not corroded by the sample. 

627. Procedure in the field. — The area for survey 
having been selected, the field party — which usually 
consists of two men, a chief and an assistant — proceeds 
to examine the soils of the district. Headquarters are 
temporarily established in a convenient village or coun- 
try residence, and excursions are made into the adjacent 
territory. The routes are laid out carefully and system- 
atically with the purpose of examining the soils of the 
entire area. The party proceeds along the highway, 
with frequent stops and side excursions into the field, 
examining the soil to a depth of three or more feet with 
the auger. In humid regions the basis of the soil classi- 
fication is a section of soil three feet deep. In arid 
regions, where alkali is prevalent, a six-foot section is usu- 
ally the basis of classification, and occasionally much 
deeper examinations are made for studying the position of 
the water table. The soil is examined especially with refer- 
ence to its texture, structure, color, drainage, content of 
organic matter, depth of different strata, and special chemi- 
cal properties such as lime and alkali. The natural vege- 
tation is observed, and note is taken of the type and 
growth of crops as well as the extent and species of forest 
trees. 

Borings and other observations are made from point 
to point as the appearance of the soil, the topography, 
the conformation of the country, and the character of the 
vegetation may suggest. The frequency and position of 
observations are determined entirely by the judgment of 
the field man. They may be made every few rods or at 



730 SOILS: PROPERTIES AND MANAGEMENT 

much wider intervals. In getting acquainted with new 
types, more borings and detailed observations are neces- 
sary than after the soil properties have become familiar 
and can be more readily identified. Where the soil is 
highly variable, much more frequent observations are 
necessary than where it is more uniform. As the survey 
proceeds the field man progresses from point to point, 
along the highway and in the field, on foot or by convey- 
ance as may be more convenient, extending his observa- 
tions about half the distance to the next highway in order 
that all the territory may be covered most conveniently. 
Usually the trip is arranged in a circuit. All areas of soil 
essentially alike in their proi)erties and plant relations are 
recognized as of the same soil type, and their position on 
the map is represented by one of the colors. As the 
observations proceed, a change in the character of the soil 
may occur. When this change becomes of such char- 
acter and importance as to cause difference in agricultural 
relations and to be recognizable under the i)lan of classi- 
fication outlined above, a new type is recognized. The 
boundary line between the two types must be carefully 
traced out by observation and by borings. As the work 
proceeds other types of soil may be recognized and the 
boundaries are determined and represented on the map, 
each type being indicated by a particular color or symbol. 
A large number of types of soil may be recognized in each 
area surveyed. The character and relationships of these 
must be studied carefully in order to decide how they 
may be grouped in series and larger units. 

In practice it is usually better for the field i)arty to 
first make general observations over the area, in order 
to recognize the main di\isions of the soil that may later 
require subdivision into types. To this end all a\ailable 



THE SOIL SURVEY 731 

facts, particularly concerning the geology of the region, 
should be familiar to the survey man before active field 
work is begun. It is easier and results in a greater degree 
of accuracy to first recognize the larger divisions of an 
area of soil, and later work out the types, than to be con- 
cerned from the very beginning entirely with these ele- 
mental subdivisions. 

During the progress of the field observation the rela- 
tionship of each type of soil to natural and cultivated 
plants should be studied, and the tillage properties of the 
soil noted. The farmers also may be interviewed con- 
cerning their soils, as to tillage properties, crop relations, 
and response to methods of improvement. In short, all 
available data concerning the character of the soils of the 
region should be sought. 

Records are made in the field notebook descriptive of 
the average character of each type of soil. The descrip- 
tion of typical borings may be recorded and their location 
noted on the map. Preliminary samples may be taken 
and sent to the central laboratory for physical or chemical 
examination, to check the judgment of the field man. 

628. Collection of soil samples. — Samples of soil for 
laboratory examination should be taken only after the 
field man is thoroughly familiar with each type of soil 
and can select a location that accurately represents the 
average material of the type. Attention should be given 
to the slope, drainage, abnormal modifications, and 
manurial treatment of the soil at that point. Therefore, 
in survey work samples are collected only in the latter 
part of the season. One or more samples of each im- 
portant type of soil are taken. The material, to the 
amount of a quart, is preserved in cloth bags. Usually 
each sample is divided into two parts, one representing 



732 SOILS: PROPERTIES AND MANAGEMENT 

the soil and the other the subsoih If there is a marked 
change in appearance or texture in the subsoil, other divi- 
sions of the sample may be made. Usually a composite 
of a number of borings over an area of several square 
rods, or even of several acres, may be necessary in order 
to secure an accurate sample and to obtain enough ma- 
terial. A composite of several representative borings 
made over a considerable area gives a more nearly accu- 
rate sample than is possible in a single boring. The 
possibility of local variations is very great, and their 
effect is reduced when composite sampling is done. 

Each bag should bear a tag which is given a number 
and on which is placed the name of the type, the location 
of the sample in the section, and a brief description of the 
material. The same data are recorded in the field note- 
book, which is finally preserved as a part of the permanent 
office record of the survey. The description in the note- 
book may be amplified more than is possible on the tag. 
The location where each sample was taken should be 
accurately marked on the field map by a number corre- 
sponding to the number of the sample. Usually each 
sample is given a number, and the parts are indicated by 
a letter, proceeding from the surface downward. Where 
the material is very wet and likely to become lumi)y 
when dry, it may be dried in a thin layer before being 
finally bagged for shipping or preser\'ation. Care should 
be bestowed on every part of the operation of collection, 
describing, numbering, tagging, tying, and shii)ping, in 
order to insure accuracy and permanency of the record. 

The soil auger is generally used in taking the sample 
and in examining the soil section. The worm of the 
auger is bored into the soil until it is filled. It is then 
withdrawn and the soil is removed. The soil may be 



THE SOIL SURVEY 733 

collected on one or more squares of oilcloth, or it may be 
placed directly in the appropriate bags. The worm of the 
auger having been cleaned, it is inserted into the same 
hole and advanced until it is again full, when it is with- 
drawn and cleaned as before. This operation is repeated 
until the desired depth is reached. Where the soil is a 
very heavy clay, it may be advisable to only partially 
fill the worm with soil. ^Vhere the soil is very dry and 
puKerizes to a dust, it may slip off the worm, in which 
case water may be added to make it adhere. The upper 
part of the hole should be cleaned, and it may be slightly 
enlarged so as to prevent contamination with the material 
from the lower part of the section. Where there is rubbish 
on the surface, this should be removed previous to begin- 
ning the collection of the sample. 

In very stony soil the auger is not suited to taking a 
sample, either for examination or for record. In such 
soil a shovel may be used, or the sample may be taken in 
a road or some other cut by means of a geologist's hammer. 

The face of the section should be removed to a depth 
of several inches, in order to eliminate weathered or con- 
taminated material which may not be typical of the soil 
section. Usually a difference in color and physical 
properties of the soil indicates a modification of the typi- 
cal material. 

629. The accuracy and detail of the soil survey. — The 
accuracy and detail of the soil survey depend on many 
things. Assuming an adequate preparation on the part 
of the field man, there are limitations in accuracy imposed 
by the scale on which the map is made and the nature of 
the soil. The smaller the scale of the map used in the 
field, the less is the detail that may be represented. The 
commonest scale employed is one inch to a mile. Some 



734 SOILS: PROPERTIES AND MANAGEMENT 

states use a larger scale, and in reconnoissance surveys 
a smaller scale is used. While a large scale increases 
the detail that may be represented, it also multiplies 
the difficulties of making an accurate classification 
because it increases the number of properties to be 
observed. 

The nature and occurrence of soils in the field involves 
more variations than can be shown on the map. The 
boundaries of soil types grade into one another, and it 
may not be possible to mark the division within several 
rods. Sometimes even a wider range occurs. The accu- 
racy with which the boundary may be determined and 
drawn depends very much on the way in which the two 
adjacent soils have been formed. If they are very dif- 
ferent, the boundary may be very distinct. Some types 
of soil are characterized by local variations in sections, 
or from point to point, which are on too small a scale to 
be recognized as a type. Variations may be induced in a 
type due to dift'erences in topography, drainage, or culti- 
A'ation. Where the properties do not bring about an 
important change in the crop relations of the soil, they 
may be ignored. Differences due to cultivation are 
generally disregarded. The soil survey is made to cover 
a period of years, and only permanent dift'erences should 
be considered. 

Variations in the soil must be considered in relation to 
the scale of the map. On a scale of one inch to a mile 
the minimum area that can be shown is about ten acres. 
Occasionally, where the dift'erence in type constitutes a 
striking contrast, the small area may be somewhat ex- 
aggerated in size. An area of muck soil having high 
value for the production of truck crops might be such an 
exception. 



THE SOIL STRVEr 735 

630. The soil survey report. — The soil survey report 
consists of two parts, the printed report and the map 
showing the distribution of the soil types. The printed 
report accompanying the soil map should be a brief- but 
comprehensive summary of the observations of the field 
party in the areas surveyed. It should cover six types of 
information: (1) location and boundaries of the area; 
(2) general physical features ; (3) climate ; (4) agricul- 
tural history and development;. (5) description of the 
soils ; (6) suggestions for improvement in the manage- 
ment of the soil that may have been determined by the 
survey. 

The description should point out the salient topographic 
forms, the range in elevation, the nature and development 
of the drainage, the transportation facilities, and the dis- 
tribution of population and of farm areas. The discus- 
sion of climate should note the monthly mean tempera- 
ture and amount of precipitation ; the character of the 
extreme ranges in these ; the direction of prevailing winds ; 
and the occurrence of any special features, such as untimely 
frosts, sleet and hail and windstorms, and the nature of 
local variations in climate that may be due to the prox- 
imity of bodies of water or topographic features. The 
agricultural history should note the source and character 
of the agricultural population, the chief products and any 
changes that have occurred in their production, and the 
present status of the area. 

The description of the soils should be in two parts. 
First, the grouping of the types into series and larger 
divisions, with the geological and topographic relations 
of these groups and a clear statement of the characteristic 
properties of each group. Any important characteris- 
tics that are common to two or more types or series, such 



786 SOILS: PROPERTIES AND MANAGEMENT 

as a deficiency in humus, lime, or drainage, should be 
pointed out. Secondly, a detailed description of each 
type following a uniform outline of properties, including 
color, texture, depth, structural peculiarities, and minera- 
logical and chemical features. Following this, attention 
should be drawn to the location and extent of the type 
in the area, and to its mode of origin, drainage conditions, 
and economic relations, including the crop rotation and 
extent of development. 

In making suggestions for the treatment of the soils a 
clear distinction should be drawn between methods of 
soil management and improvement, and questions of farm 
organization and management. The data collected by 
the soil survey man will usually lead him to confine his 
suggestions to the former group. 

631. The soil map (Fig. 84). — The soil map is de- 
signed primarily to show the geographic position and ex- 
tent of each type of soil. Therefore an accurate base map, 
showing important natural and cultural features as noted 
above, is essential. The scale of the map must be adapted 
to the amount of detail to be shown. The commonest 
scale in use in the United States is one inch to a mile. In 
reconnoissance surveys a scale of one inch to six miles is 
usually employed. The map is printed in colors or in 
symbols representing the different types of soil. Symbols 
may be added to the color to indicate further variation, 
such as the presence of much stone, occurrence of ledge 
rock, or a swampy condition. On the right-hand border 
of the map a legend to the colors or symbols is given, and 
they may be arranged in accordance with the scheme of 
classifying the soils to show their relationship. On the 
left-hand border, the character of the profile of each type 
of soil is indicated by a series of legends. 



Bui. 60, Bureau of Soils, U. S. Dept. of Agriculture. 




Volusia 
silt loam 



Volusia Duii/cirk Huntintjton Dunkirk Muck 

loam gravelly louni louvi ^i^y 



Fig. 84. — Part of the Madison County, N. Y., soil map showing the topography 
and the relation of the various soil types to one another. 



THE SOIL SURVEY 737 

632. The extent of soil surveys in the United States. — 
The detailed survey and mapping of soils by the Bureau 
of Soils of the United States Department of Agricul- 
ture, according to the scheme outlined above, has been in 
progress since 1899. On January 1, 1915, about 330,000 
square miles had been covered by detailed surveys and 
435,000 square miles had been covered by reconnoissance 
surveys. In addition, several miscellaneous surveys have 
been made in outlying provinces such as Porto Rico, 
Panama, Philippine Islands, and Alaska. The total num- 
ber of soil types and series recognized is approximately 
2000 and 600 respectiveh'. 

633. Surveys by state institutions. — Several states 
are engaged in soil survey work, either independently or 
in cooperation with the United States Bureau of Soils. 
The states that have undertaken this work independently 
have carried it out in the same general manner as in the 
Federal survey. Some of the states that are working 
independently have confined their investigations to recon- 
noissance surveys on a large scale. Tennessee has pub- 
lished a general report, with a map, on the soil areas of 
the state, with special reference to their geological rela- 
tions. Account is also taken of the texture, chemical 
composition, and other properties. Iowa, Missouri, and 
Illinois and Ohio ^ have published similar general reports 
showing soil areas based chiefly on origin. Illinois, In- 
diana, and New Jersey have also published detailed reports 
on particular areas. In their work the principles of clas- 
sification laid down above have been followed in a general 
way, but with emphasis on certain selected properties. 



^ Coffey, C. N., and Rice, T. D. Reconnoissance Soil Survey 
of Ohio. U. S. D. A., Bur. Soils, Field Op., p. 134. 1912. 
3b 



738 SOILS: PROPERTIES AND MANAGEMENT 

Illinois has given special prominence to color, and, in ad- 
dition to the general description of the soil types, includes 
data derived from chemical analyses to show the store of 
plant-food in the surface layers. The Indiana and Mis- 
souri surveys have combined a purely geological scheme of 
classification on the basis of origin, with certain properties 
of practical importance, such as texture, color, and content 
of humus, but without observing a systematic order. 
The New Jersey survey includes rather full data on the 
chemical composition of the soil types, in addition to the 
usual discussion of their properties and relationships. 

634. Surveys in other countries. — Several countries 
have undertaken some type of soil or agrogeological sur- 
vev. These surveys, which have been undertaken in 
Germany, France, Italy, Russia, Great Britain, and Japan, 
have aimed at a broad practical classification of soils 
based on their agricultural values and tillage properties. 
Several thousand square miles h-dxe been covered by the 
surveys in each of these countries. Colored charts are 
published to accompany the descriptive reports. In these 
surveys the classification is largely genetic, in combina- 
tion with a consideration of the more evident physical 
and chemical properties, which are recognized and grouped 
in the field in much the same manner as in tl\e American 
surveys. The details, of course, are considerably differ- 
ent in the reports of the different countries. In Germany 
the maps are geological-agronomic in character; that is, 
prominence is given to both the geological and the crop 
relations of the soils. Tlieir physical and chemical proper- 
ties are pointed out and are used in the classification. 
Similar methods are followed in France and Japan. 

In England the areas of soil are determined, first, by 
means of their texture ; secondly, by means of their con- 



THE SOIL SURVEY 739 

tent of humus and lime carbonate, with which color and 
drainage are associated ; and thirdly, by means of the 
geological formation and mode of origin. Fairly com- 
plete mechanical and chemical analyses of representative 
samples of the important types are included, and the rela- 
tion of the soils to crops and farm practice is discussed at 
some length. The grouping of the types into series, 
groups, provinces, and the like, is not so distinct as in the 
American surveys. That the fundamental importance 
of the larger factors in classification are recognized is 
shown in the discussion of the relation of precipitation 
and temperature to the properties and agricultural uses 
of the soil, in which the controlling influence of these 
over large areas is pointed out. 

635. Uses of the soil survey. — The soil survey is 
useful in many ways, but it is not a final investigation. 
It is to be regarded rather as a means of determining the 
status of the soil and related conditions in the field. 
These may throw light on many farm practices and lead 
to their improvement. ]\Iore frequently the soil survey 
points to lines of further investigation that should be 
carried out. 

The uses of the soil survey may be conveniently divided 
into two groups — its use to the individual, and its use 
to the state. For the individual, the soil survey (1) points 
out the character and location of the several types of soil 
on his farm which may be correlated with particular 
crops and farm practices ; (2) shows him the relationship 
of soils o^'er wide areas, which may form a basis for the 
adoption of new crops or new methods of soil manage- 
ment ; (3) provides a reliable central source of informa- 
tion concerning soil conditions ; (4) standardizes methods 
of description and representation of soils ; (5) reveals in 



740 SOILS: PROPERTIES AND MANAGEMENT 

many cases important problems of soil improvement that 
need attention ; (6) affords a guide in the exchange of 
real estate and in the selection of land for particular pur- 
poses. For the state the soil survey (1) shows its soil 
resources ; (2) by the collection of this data at a central 
point, affords the basis for the correlation of all other 
types of information, the character of which is affected 
by the soil relations ; (3) shows in man\' cases the occur- 
rence and importance of large questions of soil impro\e- 
ment, and may point out the need for further investiga- 
tions ; (4) gives a basis on which much of the results of 
experiments, investigations, and observations on soil im- 
provements, crop growth, and in many cases farm man- 
agement, should be applied ; (5) is a means of commu- 
nication and mutual understanding between the state 
institutions concerned with agricultural information and 
the individual farmer ; (6) by affording a basis of facts, 
promotes sound commercial, social, and governmental 
development. 

The soil survey is essentially an inventory of the re- 
sources in land and closely allied interests. It helps the 
farmer to understand the situation of his farm and its 
relations to other farms. It helps the state to get ac- 
quainted with its domain, and promotes a better sense of 
mutual understanding and helpfulness. The soil survey 
in some form is an essential step in sound community 
building, for the success of most interests — commercial, 
social, and institutional — rests ultimately, to a large 
extent, on the character and value of the soil. 



AUTHORS' INDEX 



Adams, G. E., Salt as fertilizer, o44. 
Ageton, C. U., Lime and magnesium, 

538. 
Aikman, C. M., Composition of manure, 
595. 
Production of manure, 597. 
Alway, F. G., Composition of humus, 

148. 
Ames, J. W., Lime in soil, 378. 

Soil investigation, 69, 70. 
Amnion, G., Hygroscopicity, 203. 
Appiani, G., Silt cylinder, 9L 
Ashley, H. E., Colloidal clay, Kil. 
Estimation of colloids, 107. 
Plasticity, 172. 
Atkinson, A., Storage of moisture in 

soil, 715. 
Atterberg, A., Classification of soil par- 
ticles, 96. 
Cohesion test, 176. 
Measurement of cohesion, 181. 
Mechanische Bodenanalyse, 84. 
Plasticity, 171. 
Silt cylinder, 91. 

Baker, M. N., Sewage irrigation, 711. 

Bancroft, W. D., Colloidal chemistry, 
153. 

Barakov, F., Carbon dioxide in soil, 409. 

Baumann, A., Composition of humus, 
133. 

Beal, W. H., Absorptive capacity of 
litter, 603. 
Handling manure, 602. 

Bennett, H. H., Classification of soils 
in U. S., 724. 

Bertrand, G., Manganese, 531. 

Biltz, W., Soil solution, 345. 

Bizzell, J. A., Composition of drainage 
water, 372. 
Legume cultures, 545. 

Blanck, E., Law of minimum, 554. 

Bolly, H. L., Disease-producing organ- 
ism, 426. 

Boullanger, E., Sulfur, 524. 



Bou.ssingault, J. B., Snow and tempera- 
ture, 306. 
Boviyoucos, G. J., Bibliography of soil 
heat, 289. 
Manure and soil temperature, 316. 
Radiation, 302, 304. 
Soil temperature, 301. 
Specific heat of soil, 295. 
Texture and conductivity, 309, 312. 
Bowie, A., Practical irrigation, 682. 
Breazeale, J. F., Acid toxicity, 379. 

Estimation of organic matter, 143. 
Brenchley, W. E., Soil solution and 

plant growth, 347. 
Briggs, L. J., Analysis of soil, 143. 
Capillary movement, 225. 
Classification of particles, 96. 
Hygroscopic and capillary water, 

208. 
Hygroscopic moisture, 206. 
Mechanical soil analysis, 84. 
Moisture equivalent, 220. 
Soil solution in situ, 343. 
Water requirements of plants, 245, 

712. 
Wilting point, 258. 
Britton, W. E., Availability of ferti- 
lizers, 510. 
Bronet, G., Penetration of fertilizers, 

354. 
Brown, B. E., Carbonized materials, 141, 
144. 
Fertilizers and acidity, 381. 
Brown, C. F., Alkali land reclamation, 

399. 
Brown, C. W., Bacteria in soil, 439. 
Brown, P. E., Bacteria in soil, 432. 
Bryan, H., Soil analysis, 93. 
Buckingham, E., Capillary movement, 
232. 
Capillary Water, 217. 
Diffusion of gases in soil, 483. 
Movement of water vapor in soil, 

241. 
Natural mulching, 277. 



741 



742 



authors' index 



Buckman, H. O., Formation of residual 
clay, 25. 
Moisture control, 279. 
Storage of .soil moisture, 715. 
Buddin, W., Partial sterilization of soil, 

471. 
Burmcster, H., Temperature of soil, 321. 
Burr, W. W., Storage of soil moisture, 
715. 

Caldwell, ,1. S., Wilting point, 258. 
Cameron, F. K., Estimation of organic 
matter, 143. 
Litmus paper test, 380. 
Physical condition of soil, 181. 
Soil solution, 346. 
Solubility of phosphates, 358. 
Test for cohesion, 176. 
Campbell, H. W., Dry-farming, 712. 
Carpenter, L. C, Measurement of 

water, 707. 
Gates, J. S., Mulch and moisture, 280. 
Cato, M. P., Land drainage, 629. 
Chamberlin, T. C, Driftless area, 67. 
Chamberlain, C. W., Molecular attrac- 
tion, 206. 
Chester, F. D., Bacteria in soil, 432. 
Chilcott, E. C, Dry-farming, 712. 
Christie, G. L, Soil survey of Iowa, 718. 
Clark, F. W., Data of geochemistry, 5, 
24, 72. 
Composition of loess, 59. 
Coffey, C. N., Reconnoissance survey of 
Ohio, 737. 
Classification of soils, 718. 
Conn, H. J., Bacteria in soil, 431. 
Goppenrath, E., Catalytic agents, 529. 
Coville, F. W., Acid-tolerating plants, 

384. 
Coville, J. v.. Acids in plants, 379. 
Cox, H. R., Mulch and moisture, 280. 
Craig, C. E., Weeds and crop growth, 

281. 
Crosby, W. O., Colors of soils, 76. 
Cushman, A. S., Air elutriator, 86. 
Colloids, 161. 
Plasticity, 172. 
Czapek, J., Solvent action of roots, 406. 
Czermak, W., Hygroscopic coefficient, 
190. 

Darwin, G., Earthworms, 19, 422. 
Daubrec, A., Solubility of orthoclase, 24. 
Davis, N. B., Plasticity, 172. 
Davis, R. O. E., Electrical bridge, 728. 
Salts and capillarity, 229. 



Deh6rain, P. P., Lime and phosphorus, 

536. 
Demelon, A., Sulphur, 525. 

Penetration of fertilizers, 354. 
Digby, K., Mineral manure, 490. 
Diller, G. S., Composition of limestone 
soil, 66. 

Residual clay, 27. 
Dobeneck, A. F. von. Absorption, 367. 

Hygroscopicity, 203, 207. 
Dorsch, F., Availability of fertilizers, 510. 
Dorsey, C. W., Alkali land reclamation, 
399. 

Composition of alkali, 393. 
Duchacek, F., Bacteria in soil, 437. 

Fermentation and phosphates, 520. 
Dugardin, M., Sulfur, 525. 
Dupr6, H. A., Capillary movement, 231. 
Dyer, B., Citric acid method soil an- 
alysis, 336. 

Plant food in Broadbalk field, 337. 

Ebermayer, E , Temperature of soil, 322. 
Ehrenberg, P., Effect of soil antiseptics, 

470. 
Estimation of colloids, 168. 
Eichhorn, H., Absorption by chabazite, 

3.56. 
Elliott, C. G., Land drainage, 627, 629. 

659. 
Size of tile, 651. 
Ernest, A., Carbon dioxide production, 

139, 408. 
Etcheverry, B. A., Linings for canals, 

694. 

Failyer, G. H., Absorption by soils, 351. 

Composition of soil, 70. 

Minerals in soil separates, 101. 
Faure, L., Land drainage, 627. 
Feilitzen, H. von. Sulfur, .525. 
Fippin, E. O., Causes for granulation, 188. 

Classification of soils, 718. 
Fletcher, C. C., Soil analysis, 93. 
Flugel, M., Law of minimum, 554. 
Forbes, R. H., Irrigation, 686. 
Fortier, S., Application of irrigation 
water, 695. 

Mvilchos under irrigation, 705. 

Orchard irrigation, 682. 

Small water supply, GS2. 
Frank, B., Effect of heat on soluble 

matter, 466. 
Fraps, J. S., Availability of phosphatee, 
338. 

Fertilizers, 546. 



AUTHORS' INDEX 



743 



Frear, W., Losses of manure, 005. 
Fred, E. B., Effect of soil antiseptics, 

408. 
French, H. F., Drainage, 629. 
Freundlich, H., Kapillar chemie, 153. 
Friedlander, K., Soil antiseptics, 470. 

Gaither, E. W., Lime in soil, 378. 
Soil investigation, 69, 70. 

Gallagher, F. E., Absorption of gases, 
367. 
Cohesion tests, 176. 
Physical condition of soil, 181. 
Temperature and hygroscopicity, 
208. 

Gardner, F. D., Fertilizers and acidity, 
381. 

Gedroiz, K. K., Phosphate fertilizer, 519. 

Geikie, A., Geology, text of, 40. 

Georgeson, C. C, Manure and soil tem- 
perature, 316. 

Gerlach, U., Composition of drainage 
water, 350. 
Drainage water, 370. 

Gieseker, L. F., Storage of soil moisture, 
715. 

Gilbert, J. H., Composition of drainage 
water, 240. 

Gile, P. P., Lime and magnesium, 538. 
Nitrogen in plant nutrition, 491. 

Girard, .\., Soil anti.septics, 465. 

Goddard, L. H,, Co.st of drainage, 655. 

Goessman, C. A., Poultry manure, 589. 

Golding, J., Partial sterilization, 474. 

Grandeau, L., Estimation of humus, 144. 

Greig-Smith, R., Effect of partial ster- 
ilization, 472. 

Haberlandt, H., Cohesion test, 175. 

Heat and germination, 290. 
Hall, A. D., Accumulation of soil nitro- 
gen, 463. 

Classification of soil particles, 96. 

Classification of soils, 718. 

Composition of crops, 418. 

Composition of drainage water, 369. 

Composition of manure gases, 594. 

Crop adaptation and texture, 105. 

Denitrification, 4.57. 

Fermentation of manure, 591. 

Losses of manures, 600. 

Losses of nitrates, 454. 

Losses of nitrogen, 500. 

Lysimeter records, 266. 

Manures, 579. 

Mechanical analysis, 103. 



Hall, A. D., Nitrification, 453. 
Nitrogen fertilizers, 547. 

Residual effect of man\ires, 614. 

Soil separates, 102. 

Soil solution and plant growth, 347. 

The Soil, 11. 
Halligan, J. E., Composition of rotted 
manure, 596. 

Fertilizers, 546. 
Hart, R. A., Alkali land reclamation, 
399. 

Handling manure, 602. 

Sulfur as a fertilizer, 520. 
Hartwell, B. L., Acidity test, 387. 

Fermentation and phosphates, 520. 
Hasenbaumer, J., Catalytic agents, 529. 

Colloidal chemistry, 153. 
Hassler, C, Colloid chemistry, 153. 
Headden, W. P., Nitrates in alkali soil, 

292. 
Heinrich, R., Hygroscopic coefficient, 

257. 
Heinze, B., Soil antiseptics, 470. 
Hellriegel, H., Water requirement of 

plants, 246, 249, 250. 
Henneberg, W., Absorbed bases, 3.54. 

Absorption, 353. 
Henry, W. A., Production of manure, 588. 
Hess, E. H., Lime, 541. 
Hess, R. H., Social aspect of irrigation, 

691. 
Hilgard, E. W., 79, 82. 

Absorption and temperature, 367. 

Alkali land reclamation, 399. 

Churn elutriator, 88. 

Composition of alkali, 393. 

Dilution of plant food in soil, 332. 

Estimation of humus, 144, 147. 

Retentive power of soil for water, 221. 

Roots and humus, 127. 

Soil analysis, 96. 

Soil and climate, 62, 72. 

Soils of arid and humid regions, 71. 

Temperature and hygroscopicity, 
208. 

Vegetation and soil classification, 
720. 
Hills, J. L., Commercial fertilizers, 562. 
Hiltner, L., Effect of soil antiseptics, 469. 
Hoffman, C, Fermentation and phos- 
phates, 520. 
Hopkins, C. G., Tvibrary system of soil 
naming, 726. 

Manure and the rotation, 616. 

Nitrogen storage by legumes, 621. 

Soil survey of Illinois, 719. 



744 



AUTHORS' INDEX 



Houston, H. A., Estimation of humus, 

142. 
Hunt, T. F., Manure and the rotation, 
616. 
Nitrogen fertilizers, 547. 
Hutchinson, H. B., Nitrogen assimila- 
tion, 495. 
Organic matter in soil, 1.'56. 
Partial sterilization of soil, 470. 

Jenkins, E. H., Availability of fertilizers, 
510. 
Commercial fertilizers, 564. 
Jodidi, S. L., Nitrogen compounds, 133. 
Johnson, S. \V., Availability of fertilizers, 
510. 
Composition of soil air, 477. 
Johnston, J., Early drainage in America, 

630. 
Jones, C. H., Commercial fertilizer, 502. 

Kellerman, K. F., Lime, 537. 

Nitro-cultures, 462. 

Litmus test, 386. 
Kellev, W. P., Ammonia as plant food, 
" 495. 

Magnesium and nitrates, 536. 
Kellner, O., Ammonia as plant-food, 495. 
Kelly, M. P., Manganese, 530. 
Kerr, W. C, Composition of marl, 38. 
Kiesselbach, T. A., Water requirement 

of corn, 248. 
King, F. H., Absorption and produc- 
tivity, 368. 

Aspirator, 124. 

Capillary and ground water, 214. 

Capillary movement, 225. 

Drainage and soil temperature, 314. 

Drainage and free water, 237. 

Effect of barometric pressure, 234. 

Effective diameter of soil particles, 
123. 

Effective surface of soil particles, 
125. 

Irrigation, 682. 

Land drainage, 627. 

Movement of ground water, 235. 

Pore space in soil, 116, 117. 

Slope and soil temperature, 319. 

Spring plowing, 284. 

Surface tension and temperature, 227. 

Temperature and hygroscopicity, 
208. 

Water requirement of plants, 247. 

Wind breaks and moisture, 285. 
Kianison, C. S., Plasticity, 171. 



Kinsley, A. F., Bacteria in soil, 432. 
Klippart, J. H., Land drainage, 627. 
Knisely, A. L., Acid soil, 383. 
Koch, A., Theory as to effect of anti- 
septics, 468. 
Konig, J., Catalytic agents, .529. 

Colloid chemistry, 153. 
Kostytscheff, M. P., Roots and humus, 

127. 
Krober, E., Bacteria in soil, 438. 

Fermentation and phosphates, 520. 
Kiimmel, .\. B., Soil and geological 
surveys, 719. 

Lang, C, Radiation, 302. 

Lapham, J. E., Classification of soils of 

United States, 724. 
Lapham, M. H., Classification of soils 
of United States, 724. 
Capillary movement, 225. 
Lawes, J. B., Composition of drainage 
water, 240. 
Nitrogen in plant nutrition, 491. 
Leather, J. W., Water requirements of 

plants, 247. 
LeClerc, J. A., Acid toxicity, 379. 
Liebenberg, R. von. Specific heat of 

soils, 294. 
Ijebig, J. J. von. Composition of plants, 
491. 
Law of minimum, 553. 
Solvent action of root«, 405. 
Lint, H. C, Sulfur and soil acidity, 382. 
Lipman, C. B., Bacteria in arid soils, 73. 
I>ipman, J. G., Availability of fertilizers, 
510. 
Fermentation of manure, 591. 
Green manures, 619. 
Loew, O., Lime and magnesia, 538. 
I>ohnis, F., Bacteria in soil, 438. 
Loughridge, R. H., Crop tolerance to 
alkali, 395. 
Distribution of irrigation water in 

soil, 704. 
Hygroscopic water, 204. 
Soil separates, 102. 
Lynde, C. J., Capillary movement, 231. 
Lyon, T. L., Composition of drainage 
water, 372. 
Legume cultures, 545. 
Lysimeter tanks, 241. 

McBride, F. W., Estimation of humus, 

142, 144. 
McCall, A. G., Solution of .'•oil in situ, 

344. 



authors' index 



745 



McCaughey, W. J., Color of soil, 77. 

Soil-formint; minerals, 100. 
MacDonald, W., Dry-fariuing, 712. 
McLane, J. W., Moisture equivalent, 
220. 

Soil -solution in situ, 343. 
McLaughlin, W. W., Capillary move- 
ment, 224. 

Movement of irrigation water, 704. 
Marbut, C. F., Classification of soils of 
United States, 718, 724. 

Soils of United States, 34. 
Marchal, E., Ammonification, 447. 
Mares, M. N., Sulfur, 52.5. 
Mayer, A., Optimum moisture, 263. 
Mayo, U. S., Bacteria in soil, 432. 
Maz£, P., Law of minimum, 554. 
Mead, E., Extent of irrigation, 685. 

Irrigation institutions, 682. 

Legal status of irrigation, 691. 

Lining for canals, 694. 

Preparation for irrigation, 682. 
Mellen, C. R., Drainage of Johnston 

farm, 630. 
Merrill, G. P., Color of soil, 77. 

Residual clay, granite, 27. 

Rock weathering, 13, 26, 62. 

Weathering of gneiss, 66. 

Zeolitis, 357. 
Merrill, L. A., Irrigation of crops, 682. 
Merzbacher, C, Origin of loess, 60. 
Miles, M., Drainage in Europe, 629. 
Miller, N. H. J., Nitrogen assimilation, 
495. 

Organic matter in soil, 136. 
Miner, H. L., Commercial fertilizers, 562. 
Mitscherlich, A. E., Estimation of 
colloids, 168. 

Hygroscopicity, 208. 

Law of Minimum, 5.53. 

Water and plant growth, 253. 
Molisch, H., Enzymes of roots, 407. 
Montemartini, L., Catalysis, 530. 
Montgomery, E. G., Water require- 
ments, 245, 248, 249. 

Water requirement of corn, 251. 
Mooers, G. A., Soil survey of Tennessee, 

719. 
Mulder, T. J., Organic matter of soil, 131. 
M Ciller, R., Solubility of minerals, 24. 

Newell, F. H., Irrigation, 682. 
Niklas, H., Colloid chemistry, 153. 
Norton, J. H., Composition of surface 

water, 373. 
Noyes, A. A., Properties of colloids, 153. 



Oberlin, C, Soil antiseptics, 465. 
Olin, W. H., American irrigation, 682. 
O.sborne, T. B., Beaker method of 
mechanical analysis, 96. 
Classification of soil particles, 90. 

Paddock, W., Irrigation of fruit, 682. 
Pagnoul, M., Effects of carbon bisul- 
fide, 466. 
Parks, J., Drainage and soil tempera- 
ture, 314. 
Patten, A. J., Bacteria in soil, 439. 
Patten, H. E., Absorption of gases, 367. 
Absorption by soils, 351. 
Heat of conden.sation, 209. 
Heat transfer, 309, 313. 
Specific heat of soil, 295. 
Temperature and hygroscopicity, 
208. 
Patterson, H. J., Lime, 541. 
Peake, W. A., Estimation of organic 

matter, 143. 
Pember, F. R., Fermentation and phos- 
phates, .520. 
Penny, C. L., Clover as green manure, 
621. 
Green manures, 619. 
Penrose, R. A. F., Composition of resid- 
ual soil, 33. 
Peters, E., Absorbed bases, 354. 

Absorption of potassium, 3.50. 
Petonson, W. H., Sulphur as fertilizer, 

526. 
Petit, A., Temperature of soil, 300. 
Pettit, J. H., Soil survey of Illinois, 

719. 
Pfaundler, L., Specific heat of soil, 294. 
PfeifTer, T., Effect of soil antiseptics, 470. 
Law of minimum, 554. 
Carbon dioxide as soil solvent, 409. 
Pick, H., Estimation of colloids, 108. 
Pickel, G. M., Composition of muck, 

37. 
Piper, C. v.. Green manures, 619. 
Pitra, J., Bacteria in soil, 437. 

Fermentation and phosphates, 520. 
Plummer, J. K., Acid materials, 376. 
Potts, E., Texture and conductivity, 309. 
Pranke, E. J., Cyanamid, 503. 
Prianischnikov, D., Availability of phos- 
phorus, 518, 521, 535. 
Puchner, H., Cohesion test, 176. 

Composition of soil separates, 102. 
Measurement of cohesion, 178. 
Pugh, E., Nitrogen in plant nutrition, 
491. 



746 



AUTHORS INDEX 



Rafter, G. W., Sewage irrigation, 711. 
Ramann, E., Carbon dioxide in soil air, 
480. 

Colloid chemistry, 153. 
Reed, H. S., Oxidation by roots, 407. 

Toxic material in soils, 136. 
Reid, F. R., Catalysis, 529. 
Rice, T. D., Reconnoissance, 737. 
Riehthofen, F., Character of loess, 59. 
Roberts, I. P., Losses of manure, 599. 

Production of manure, 587. 
Robinson, F. R., Lime, 537. 
Robinson, F. W., Root nodules and 

nitrogen storage, 021. 
Robinson, T. R., Litmus test, 380. 
Robinson, W. O., Color of soils, 77. 

Manganese, 531. 
Rodewald, H., Estimation of colloids, 

108. 
Rostworowski, S., Absorption by per- 

mutite, 357. 
Russell, E. J., Plant food elements, 3. 

Classification of particles, 90. 

Classification of soils, 718. 

Crop adaptation and texture, 105. 

Mechanical soil analysis, 103. 

Nitrogen fertilizers, 547. 

Partial sterilization of soils, 470. 

Sewage sick soils, 474. 
Russell, I. C, Subaerial deposits, 62. 

Sachs, J., Solvent action of roots, 400. 
Sackett, W. G., Ammonification, 440. 

Availability of fertilizers, 511. 
Salisbury, R. D., Driftless area, 07. 

Glacial geology, 47. 
Sanborn, J. W., Roots of crops, 81. 
Sargent, C. L., Acidity tests, 387. 
Saussure, T. de. Composition of plants, 

490. 
Schantz, H. L., Water requirements, 
245, 712. 

Wilting point, 258. 
Schlicter, C. S., Effective diameter of 

particles, 123. 
Schone, E., Elutriator, 87. 
Schreiner, C)., Absorption by soil, 351. 

Carbonized material in soil, 141, 144. 

Composition of humus, 134, 130. 

Organic substances in soil, 132. 

Oxidation by roots, 407. 
Schiibler, G., Cohesion test, 175. 
Schucht, F., Mechanische Bodenunter- 

suchung, 84. 
Schuize, B., Temperature of soil, 321. 
Schuize, F., Water extract of soil, 341. 



Schutt, M A., Losses of manure, 583, 

599, 600. 
Seelhorst, C. von. Water requirements, 

251, 255. 
Sheppard, J. H., Roots of crops, 82. 
Sherman, C. W., Soil survey of Indiana, 

719. 
Shorey, E. C, Creatinine, 497. 

Organic sub.stances in soil, 132. 
Shutt, F. T., Nitrogen storage by leg- 
umes, 021. 
Simniormacher, W., Lime and phos- 
phates, 530. 
Skinner, J. J., Creatinine, 497. 
Organic matter in soil, 130. 
Smith, C. D., Root nodules and nitrogen, 

storage, 021. 
Smith, R. E., Bacteria in frozen soil, 433. 
Snyder, H., Ash of humus, 145. 
Complete solution of soil, 330. 
Composition of humus, 149. 
Production of humus, 140. 
Spillman, W. J., green manures, 019. 
Stevenson, W. H., Soil survey of Iowa, 

718. 
Stewart, J. B., Moisture control, 285. 

Capillary movement, 225. 
Stohman, F., Absorption, 353, 354. 
Stokla.sa, J., Bacteria in soil, 437, 439. 
Carbon dioxide production, 139. 
Carbon dioxide production in soil, 

408. 
Carbon dioxide in soil air, 479, 482. 
Fermentation and phosphates, 520. 
Storer, F. H., Farm manure, 578. 
Green manure, 619. 
Humus and capillarity, 219. 
Poultry manure, 588. 
Stormer, K., Effect of soil antiseptics, 

469. 
Stover, A. P., Carey Act, 688. 
Strcmme, H., Estimation of colloids, 

107. 
Sullivan, M. X., Catalysis, 529. 

Manganese, 531. 
Swezey, G. D., Temperature of soil, 321, 
485. 

Teel, R. P., Losses of irrigation water, 

694. 
Ten Eyck, A. M., Roots of plants, 81. 
Thaer, W., Properties of colloids, 153. 
Thome, C. E., Application of manure, 
607. 
Cement versus dirt floors, 604. 
Effect of food on manure, 582. 



AUTHORS INDEX 



747 



Thome, C. E., Farm manure, 581. 

Losses of manure, 599. 

Manure and the rotation, 616. 

Production of manure, 587. 

Reinforcing manure, value, 610. 

Value of manure, 590, 601. 
TrowbridKC, A. C, Classification of sedi- 
ments, 31. 
Truog, E. A.. Sulfide test for soil acidity, 

387. 
Tularkov, N., Classification of soils, 718. 
TuU, Jethro, Effects of tillage. 490. 

Ulrich, R., Specific heat of soil, 295. 
Underwood, T. M., Soil solution and 
plant growth, 347. 

Vail, C. E., Composition of humus, 148. 
^'an Bemmelen, J. M , Adsorption, 359. 
Colloids, 101. 
Colloidal hunms, 365. 
Colloidal material, 346. 
Color of soil, 77 
Composition of humus, 133. 
Estimation of colloids, 167. 
Soil solution, 345. 
Van Slvke, L. L., A general fertilizer, 
571. 
Composition of manure, 584. 
Fertilizers, 546. 
Fertilizer mixtures, 565. 
Production of manure, 587. 
Van Suchtelen, F. H. H., Soil solution in 

situ, 344. 
Veitch, F. P., Complete solution of soil, 
330. 
Composition of soil, 66. 
Test for acidity, 390. 
Voelcker, J. A., Composition of rotted 
manure, 596. 
Manure, 579. 
Soil acidity, 383. 
Von Engeln, O. D., Glaciation and agri- 
culture, 70, 71. 
Voorhees, E. B., Availability of fer- 
tilizers, 510. 
Poultry manure, 588. 

Waggaman, W. H., Absorption by soil, 

351. 
U'agner, F., Conductivity in soil, 310. 

Manure and soil temperature, 316. 

Texture and conductivity, 309. 
Wagner, H,, Law of minimum, 553. 
Wagner, P., Availability of fertilizers, 

510. 



Wahnschaffe, F., Silt cylinder, 92. 
Warington, R., Causes of granulation, 
186. 
Colloids, 161. 
Composition of crops, 418. 
Composition of drainage water, 240. 
Denitrification, 456. 
Estimation of organic matter, 143. 
Evaporation losses, 271. 
Lime and granulation, 194. 
Nitrification, 453. 
Snow and soil temperature, 306. 
Warren, G. M., Marsh land drainage, 

627. 
Waters, H. J., Lime, 541. 
Watson, G. C, Production of manure, 

587. 
Way, J. T., Absorption by soil, 355. 

Colloids, 161. 
Weir, W. W., Soil acidity, 383. 

Test for carbonates, 388. 
Welitschkowsky, D. von. Temperature 

and movement of water, 234. 
Wheeler, H. J., Acid-tolerating plants, 
38. 
Acidity tests, 387. 
Forms of lime, 542. 
Plants injured by acidity, 385. 
Salt as a fertilizer, 544. 
Wheeler, W. P., Poultry manure, 582. 
Whipper, O. B., Irrigation of fruit, 682. 
Whitbeck, R. H., Glaciated and residual 

soils, 70. 
Whitney, M., Appp,rent specific gravity, 
il4. 
Soil cla.sses, 104. 
Soil solution, 346. 
Specific gravity of soil, 113. 
Whitson, A. R., Soil acidity, 383. 

Test for carbonates, 388. 
Wickson, J. A., Irrigation of fruit, 682. 
Widtsoe, J. A., Amount of water to 
apply, 710. 
Capillary movement, 224. 
Dry-farming, 712. 
Dry matter and water, 254. 
Irrigation water and yield, 708. 
Movements of irrigation water, 704. 
Principles of irrigation, 682. 
Storage of water in soil, 709. 
Water requirement of plants, 248, 
251. 
Wiegner, G., Absorption by permutite, 

357. 
Wiley, H. W., Complete solution of soil, 
328. 



748 



AUTHORS' INDEX 



Wiley, H. W., Estimation of organic 

matter, 143, 144. 
Mechanical soil analysis, 84, 92. 
Soil analysis, 338. 
Willcox, O. W., Soil survey of Iowa, 718. 
Williams, H. F., Soil-forming minerals, 

100. 
Williams, M. B., Irrigation in humid 

regions, 690. 
Wilson, H. M., Irrigation engineering, 

692. 
Wing, H. H., Losses of manure, 599. 

Production of manure, 587. 
Winton, A. L., Commercial fertilizers, 

564. 
Wolff, E., Composition of manure, 595. 
Wollny, E., Capillary movement, 226, 

228, 230. 



Wollny, E., Capillarity and temperature, 

214. 
Color and temperature, 302. 
Composition of soil air, 139. 
Effect of earthworms, 422. 
Gravitational movement of water, 

234. 
Optimum moisture, 262. 
Roots and humus, 127. 
Slope and temperature, 319. 
Water requirements of plants, 246. 
Water and soil temperature, 315. 
Woodward, S. M., Land drainage by 

pumping, 627. 

Yoder, P. A., Centrifugal elutriator, 89. 
Zsigmondy, R., Colloid chemistry, 153. 



INDEX 



Absolute specific gravity of minerals, 
112. 

of soil, 113. 

of soil particles, 113. 
Absorption by the soil, 349. 

causes, 355. 

formation of insoluble substances, 
358. 

influence of chabazite, 356. 

influence of colloids, 165, 350, 360. 

influence of organic matter, 150, 365. 

influence of silicates, 363. 

influence of zeolites, 355. 

influence on soil analysis, 340. 

insolubility of absorbed substances, 
354, 358. 

of ammonia, 366. 

of carbon dioxide, 366. 

of gases, 366. 

of heat, 300. 

of nitrogen and oxygen, 367. 

of phosphoric acid, 357. 

relation to temperature, 367. 

relation to drainage, 368. 

relation to productiveness, 368. 

selective, 362. 

time necessary, 353. 
Absorptive power of different plants, 

414. 
Absorbed bases, solubility of, 354. 
Abundance of common minerals, 11. 

of plant-food elements, 5. 
Acetic acid secreted by roots, 408. 
Acid, a flocculating agent, 159. 

in plant juices, 336. 

rocks, 7. 

soils, 375. 

soils caused by ammonium sulfate, 
499. 

test for carbonates, 388. 
Acidity and climate, 382. 

and colloids, 165. 

and forests, 380. 

and sulfur, 382. 

and plants indicating, 382. 



Acidity, effect on phosphate fertilizer, 
519. 

relation to bacteria, 436. 

relation to fertilizers, 381. 

quantitative determinations, 389. 

tests for, 386. 
Acid phosphate, 514. 

for reinforcing manure, 610. 
Acids formed from fermenting manure, 
593. 

in plant juices, 379. 

secreted by plant roots, 408. 
Acme harrow, 677. 
Adobe, aeolian soil, 47, 59. 

described, 61. 

wind origin, 16. 
.Eolian soils, deposition of, 58. 

adobe, 61. 

composition of, 60, 62. 

distribution, 61. 

loess, 59. 

sand dunes, 63. 
Aeration and denitrification, 456. 

and toxic materials, 133. 

effect of drainage on, 631. 

effect on nitrification, 452. 

influence on decay, 129. 

promoted by soil organisms, 422. 
Aerobic bacteria, 433. 

bacteria and decay, 444. 

fermentation of manure, 592. 
Agencies of rock decay, 14. 
Agricere in soil, 275, 472. 
A\T of the soil, 475. 

analyses, 478, 139. 

carbon dioxide, 139, 478. 

composition of, 477. 

control of, 486. 

effect of organic matter on, 139, 476. 

effect of soil moisture on, 476. 

effect of texture, 475. 

effect of tillage, 487. 

function of, 480. 

movement of, 483. 

volume, 475. 



749 



750 



INDEX 



Air-slaked lime, 539. 
Algae, aid to nitrogen fixation, 464. 
Alinit, nitro-culture, 463. 
Alkali in soils, 392. 

accumulation of, 397. 

and irrigation, 397. 

and the mulch, 282. 

block alkali, 392. 

composition, 393. 

correction, 399. 

control, 402. 

effect on plants, 394. 

effect of method of irrigation, 706. 

formation of, 724. 

outfit for testing, 728. 

salts in soil, 391. 
Alkali land, drainage of, 659. 
Alkali land.s, management of, 399. 
Alkali lands of foreign countries, 398. 
Alkali spots, 402. 
Alluvial soils, described, 39. 

distribution of, 41. 

humus and nitrogen in, 148. 
Altcrnaria, disease organism, 426. 
Alternate cropping, 714. 
Aluminum, 6. 
Aluminum phosphate, 337. 
Aluminum in soil separates, 102. 
Amendments of the soil, 534. 
' calcium sulfate, 542. 

calcium carbonate, 540. 

caustic lime, 539. 

common salt, 543. 

effect on nitrification, 536. 

effect on tilth and bacteria, 534. 

effect on toxic materials, .537. 

liberation of plant-food, 535. 

lime and granulation, 193. 

muck, 545. 
Amid nitrogen, plant-food, 497. 
Ammonia, absorption of, 353, 366. 

as plant-food, 494. 

from plant decay, 139. 

salts and acidity, 381. 

test for acidity, 387. 
Ammonification in soil, 446. 
Ammonification, effect of partial ster- 
ilization, 470. 
Ammonium sulfate, as fertilizer, 499. 
Amount of water to use in irrigation, 710. 
Anaerobic bacteria, 433. 
Anaerobic bacteria and putrefaction, 

444. 
Anaerobic fermentation of manure, 593. 
Analysis, mechanical, of soil, 97, 104, 
107. 



Analysis, mineralogical, 100. 

of adobe, 62. 

of air, 139, 478. 

of alkali, .393. 

of arid and humid .soils, 72, 147. 

of coastal plain soils, 70, 66. 

of crops, 419. 

of cumulose .soil, 37. 

of cyanamid, .503. 

of drainage water, 351, 371, 374, 500. 

of gases from manure, 594. 

of glacial soils, 68, 70. 

of granite and residual soil, 27. 

of humus, 149. 

of humus ash, 14.5. 

of limestone and residual clay, 27, 33, 
68. 

of litter, .580. 

of loess, 60. 

of manure, 581, 582, 583, .584, 588, 
.595. 

of marl, 38. 

of residual soils, 66, 68, 70. 

of .soils, humus, 147, 148. 

of soil, organic matter, 146. 

of soil separates, 101, 102. 

of water extract, 348. 
Animals, capacity to produce manure, 
587. 

effect on granulation, 192. 

effect on composition of manure, 
.581, 582, 584. 

soil-forming agent, 18. 
Antiseptics, treatment of soil with, 465. 
Apatite, mineral, 9. 

as a fertilizer, 512. 
Apophyllite, solubility, 339. 
Apparent specific gravity, 113. 
Application of water, time, 709. 
Arginine, plant-food, 497. 
Arid and humid soils, 71. 

composition of, 72. 

properties of, 72, 82. 

soil particles, composition of, 100, 
101. 
Arrangement of soil particles, 108. 
.Artificial mulch, 273. 
.Vsh composition of humus, 145. 
.\sh constituents of plants, 416. 
Aspergillus niger in soil, 427. 
.Mmospheric pressure affects soil air, 

484. 
Attraction of soil particles, 206. 
Auger, for soil examination, 727, 732. 
Augite, 9. 
Availability of organic fertilizer, 510. 



INDEX 



751 



Availability of plant-food and bacteria, 

428." 
Availability of soil water, diagram, 2(12. 
Azotobacter bacteria, 464. 

Bacillus, denitrificans, alpha and beta, 
456. 

mesentericus, reducing organism, 45.'). 

mycoides, reducing organism, 455. 

peslifer, reducing organism, 455. 

radicicola, 459, 545. 

rndiobacter, 464. 

ramosus, reducing organism, 455. 

subtilis, reducing organism, 455. 

vuloatus, reducing organism, 455. 
Baclc furrow, 671. 
Bacteria and ammonification, 446. 

and plant decay, 129. 

and root nodules, 458. 

carbon dioxide production, 408. 

conditions for growth, 433. 

distribution, 429. 

functions, 436. 

in frozen soil, 431. 

influence of sulfur on, 525. 

influence on organic matter, 435. 

inoculation with, 460. 

nitrate reduction, 455. 

number in soil, 430. 

nitrogen supply, 428. 

non-symbiotic, 460. 

solvent action of, 439. 
Bacteria in soil, 427, 428. 
Bacterial action, effect on phosphates, 

520. * 

Bacteroids, 460. 
Bacterium ellenbachensis, 403. 
Balanced fertilizer, 551. 
Barnyards, covered for manure, 605. 
Barometric pressure and drainage, 234. 
Ba.salt, 8. 

Bases absorbed, solubility of, 354. 
Bases, absorbed by colloids, 165. 
Bases and toxicity, 379. 
Bases in plant ash, 378. 
Bases, removed in drainage, 378. 
Basic rocks, 7. 
Basic slag phosphate, 513. 
Basic soil, effect on phosphates, 519. 
Bacillus amylobacter, 440. 
Bedding, absorptive capacity, 603. 
Biotite, 9. 

Biotite, solubility, 330. 
Black alkali, 392. 
Blood, dried, as fertilizer, 507. 
Bones as fertilizer, 511. 



Bone phosphate, 511. 

Bono tankage, 512. 

Brands of fertilizer, 555. 

Broadcasting fertilizer, 570. 

Bromberg, composition of drainage 

water, 370. 
Bureau of soils, classification of alkali, 

396. 

Calcium, 4, 6. 

Calcium carbonate, 7, 10. 

Calcium carbonate in soil, 333. 

Calcium combinations, 539. 

Calcium compounds, root action on, 406. 

Calcium cyanamid, 502. 

Calcium hydrate in fertilizer, 566. 

Calcium in soil separates, 101. 

Calcium loss in drainage, 372. 

Calcium nitrate, 505. 

Calcium phosphate, effect of bacteria on, 

439. 
Calcium salts, as amendments, effects, 

534. 
Calcium sulfate to reinforce manure, 

609. 
Calculation of air space of soils, 238, 477. 

of apparent specific gravity, 113. 

of free water, 238. 

of number of soil particles, 118. 

of pore space, 116. 

of surface of soil particles, 120. 

of wilting point, 260. 
Canals for drainage, construction, 635. 
Canals for irrigation, 693. 
Capillarity and texture, 214. 
Capillarity carries nitrates to surface, 

454. 
Capillary movement, 221. 

and alkali formation, 298. 

in wet and dry soil, 225. 

influenced by thickness of film, 223. 

influenced by surface tension, 227. 

influenced by texture, 229. 

influenced by structure, 232. 

intercepted by green manure, 624. 
Capillary water, 201, 210. 
Capillary water, amount, 213. 

and organic matter, 218. 

and structure, 217. 

and surface tension, 213. 

and texture, 214. 

estimation of, 219. 

factors affecting amount, 213. 

form of surface, 212. 

relation to plant, 261. 
Capillarity and ground water, 214. 



752 



INDEX 



Carbohydrates and nitrogen fixation, 

464. 
Carbohydrates as source of energy, 456. 
Carbohydrates in soil, 127. 
Carbon, 4, 6. 
Carbon dioxide, absorption of, 366. 

as an influence on climate, 49. 

and root action, 400, 408. 

end product of decay, 138. 

functions in soil, 481. 

in soil air, 21, 139, 410, 478. 

in atmosphere, 139. 

product of decay, 130. 

production by bacteria, 408. 

use in soil analysis, 339. 
Carbon disulfide as soil antiseptic, 46.5. 
Carbon disulfide from plant decay, 140. 
Carbonate of lime, 540. 
Carbonates of lime, effect on nitrates, 

536. 
Carbonates, acid test for, 388. 
Carbonates in earth's crust, 11. 
Carbonates, effect on soil, 482. 
Carbonation as weathering agent, 19. 
Carbonized material in soil, 140, 144. 
Carriers, in fertilizers, 555. i 

Catalytic action of soil, 528. 
Catalytic fertilizer, 528. 
Catch crops, and nitrate conservation, 

455. 
Caustic lime, 539. 

Cement pit storage of manure, 604. 
Centrifugal soil analysis, 93. 
Cephalothecium, disease organism in 

soil, 426. 
Cereals, absorptive power, 414. 
Chabazite, 356. 
Checking of losses by evaporation, 272. 

of losses by leaching, 267. 
Chemical agents of rock decay, 14. 
Chemical analysis of soil, 327. 

complete, 328. 

extraction with acids, 329. 

extraction with water, 340. 
Chemical changes due to heat, 291. 
Chemical composition of soils. See 

Analysis. 
Chili saltpeter, 498. 
Chloride of potash, 523. 
Chlorine, 6. 

Chlorine as fertilizer, 544. 
Chlorite, 9. 

Chloroform as soil antiseptic, 473. 
Cistern storage of manure, 605. 
Citric acid method, 336. 
Class, the soil, defined, 103. 



Class, the .soil, in classification, 722. 

Classification of rocks, 6. 

Classification of soil material, geological, 

31. 
Classification of soil particles, 95. 
Classification of soil, factors used, 720. 
Classification of soil, outline of, 721. 
Clostridium pastorianum, 403. 
Clay, character of separate, 98. 
Clay, colloidal, 161. 
Climate and acidity, 382. 
Climate and efficiency of fertilizer, 568. 
Climate, influence on soil, 65. 
Climate as factor in soil classification, 

724. 
Clouds, effect on radiation, 306. 
Clod crushers, 678. 
Coefficient of cohesion, 175. 
Coefficients of drainage, 651, 652. 
Coefficients of expansion of rocks, 17. 
Coefficient of friction, 229. 
Coefficient of hygroscopicity, 208. 
Coefficient of plasticity, 171. 
CoeflBcient of wilting, 257, 258. 
Cohesion defined, 173. 
Cohesion, determination, 174. 
Cohesion, control, 183, 197. 
Cohesion, factors affecting, 178. 
Cold and heat as weathering agents, 16. 
Collectotrichum, disease organism in 

soil, 426. 
Colloids in the soil, 153. 
Colloids, absorption by, 359. 

and acids, 165. 

chemistry, 153. 

effect of roots on, 411. 

estimation of, 166. 

factors affecting, 165. 

organic, 140. 

preparation of, 163. 
Colloidal humus, 1.33. 

materials, 346. 

matter, relation to phosphates, 517. 

phases, 158. 

state, 154. 
Colluvial soils described, 38. 
Color of soil, 73. 
Color of soils, due to weathering, 20. 

due to humus, 75. 

due to iron, 75. 

agricultural significance, 78. 

and temperature, 301. 
Color of arid and humid soils, 72. 

of glacial soil, 53. 

of marine soil, 44. 

of residual soil, 33. 



INDEX 



753 



Colters, types, 672. 
Commercial value of fertilizer, 560. 
Complete solution of soil, 328. 
Composition, of arid and humid soil.s, 
72. 

of animal manures, 584. 

of alkali, 391. 

of cumulose soil, 37. 

of crops, 410. 

of drainage water, 369. 

of gases from manure, 594. 

of glacial soil, 52. 

of glacial and residual clay, 68, 69. 

of humus, 131, 140. 

of horse and cov/ manure, 581. 

of loess, 60. 

of marl, 38. 

of manure litter, 580. 

of plants, 127, 418. 

of residual and marine soil, 66. 

of rotted manure, 596. 

of residual soil, 33. 

of soil in general, 2. 

of soil-forming minerals, 9. 

of soil due to weathering, 29. 

of soil separates, 101. 

of subsoil, 332. 

of soil air, 139, 477. 

of surface water, 373. 

of yard manure, 578. 
Composting manure, 613. 
Concentration and growth, 417. 
Concrete tile, 641. 
Condensation, heat of, 209. 
Conduction of heat in soil, 307. 
Conservation of moisture in irrigation, 

710. 
Convection in soil, 307. 
Coprolites as fertilizer, 512. 
Cornell tanks, composition of drainage 

water, 372. 
Cornell University, bacteria in soil, 429. 

effect of magnesium, 539. 

nitrates in soil, 451. 

production of manure, 587. 

soil inoculation, 462. 
Cottonseed meal, as fertilizer, .507. 
Cover crops and green manure, 620. 
Covered barnyards for manure, 605. 
Cow manure, composition, 584. 
Creatinine, plant-food, 497. 
Cropping, alternate in dry-farming, 714. 
Cropping, effect in soil ventilation, 488. 
Crops, composition of, 419. 

drought-resistant, 715. 

effect of alkali on, 394. 

30 



Crops, efficiency of fertilizer, 568. 

feeding power, 415. 

for green manure, 622. 

suited to basic soils, 385. 

suited to acid .soil, 384. 
Crumb structure, 109. 
Crushers and packers as soil pulverizer, 

678. 
Cultivators, t>'pes, 673. 
Cultures, mixed nitrogen-fixing, 464. 
Cultures of nitrogen-fixing bacteria, 458, 

461. 
Cumulose soils, 35. 
Cyanamid, nitrogen fertilizer, 502. 
Cyanamid in fertilizer mixtures, 566. 
Cytase, enzyme, 440. 

Dam, canvas, 701. 
Damping-off fungi in soil, 425. 
Dead furrow, objectionable, 671. 
"Dead" furrows, for drainage, 635. 
Decay of green manure in soil, 622. 

of organic matter in soil, 128. 

organic, and soil temperature, 315. 

and putrefaction, 443. 

of rocks, law of, 24. 
Decomposition of organic matter, 440. 
Decomposition of rock, 14. 
Deep-tilling plow, 667. 
Deflocculation of sodium nitrate, 499. 
Delta defined, 41. 
Denitrification, 4.56. 
Denudation, rate of, in U. S., 14. 
Denudation by Mississippi River, 15. 
Deoxidation as weathering agent, 20. 
Department of Agriculture, U. S. Nitro- 

culture, 462. 
Depth of moisture storage in soil, 710. 

for plowing, 669. 

of soil in relation to humus, 148. 

of soil mulch, 278. 

of tile drains, 646. 
Detention of plant-food in soil, 332. 
Dewey system of classification, 726. 
Diabase, 6. 

Diffusion of gases in soil, 483. 
Dihydroxystearic acid, 376. 
Diorite, 6. 

Disease of plants and moisture, 253. 
Diseases of plants, effect of lime, 536. 
Disease organisms in soil 426. 
Disease resistance, effect of phosphorus, 
550. 

effect of nitrogen, 549. 
Disintegration of rock, 14. 
Disk harrow, .single and double, 676. 



754 



INDEX 



Disk plow, 666. 

Disking to hold moisture, 714. 

Ditching machines, 649. 

Dolomite, 6, 9. 

Drag as soil pulverizer, 680. 

Drain till, quality, 640. 

Drainage and absorption, 368. 

Drainage and dcnitrification, 456. 

coefficient, 651. 

effects on soil, 630. 

effect on soil ventilation, 477, 488. 

effect on soil bacteria, 434. 

extent of need, 628. 

efficiency of fertilizer, 568. 

formation of humus, 152. 

history of development, 629. 

of irrigated and alkali land, 659. 

of land, indications of need, 627. '^ 

methods, 634. 

muck and peat soil, 658. 

promoted by soil organisms, 422. 

reclamation of alkali land, 400. 

relation to green manure practice, 
624. 

relation to colloids, 166. 

run-off checked, 269. 

systems, arrangement, 643. 

toxic materials eliminated, 137. 

use of explosives, 661. 

tile drains, 639. 

vertical, 660. 
Drainage water at Bromberg, 370. 
Drainage water, composition, 369, 351. 
Drainage water, relation of phosphates 

and carbon dioxide, 482. 
Drains, protection of joints, 642. 
Dried blood, 507. 
Drift defined, 52. 
Drought-resistant crops, 715. 
Dry-farming practices, 713. 

principles, 712. 

drought-resistant crops, 715. 

soils best suited for, 716. 

extent, 717. 
Drying and wetting, effect on granula- 
tion, 187. 
Dust mulch, 272. 

Dust mulch under irrigation, 705, 710. 
Duty of water in irrigation, 70S. 
Dynamite, drainage by means of, 661. 

Earthworms, action on soil, 19. 
Earthworms and productiveness, 422. 
Effective diameter of soil particles, 122. 
Effective surface of soil, 125. 
Effects of organic matter on soil, 150. 



Electrical production of nitrogen fer- 
tilizer, ,502. 
Elements of plant-food, 3. 
Enzymotic action of bacteria, 129. 
Enzymes, effect on plant-food, 438. 
Enzymes in roots, 407. 
Epidote, 9. 
Erosion, agencies causing, 14. 

effect of drainage, 633. 

in ditches, limits of grade, 636. 

ice as agency, 16. 

in irrigation canals, 694. 

rate of, in U. S., 14. 

wind action, 15. 
Eskers, 50. 
Evaporation and alkali, 282. 

and temperature, 314. 

and wind movement, 285. 

at Rothamsted, 271. 

from plants, 270. 

prevented by, 272. 

rainfall lost by, 271. 
Excreta from animals, 577. 
Exhaustion of soil, 419. 
Expansion of minerals by heat, 16. 
Explosives, drainage by means of, 661. 

Factors for plant growth, 3. 

Factory-mixed fertilizer, 563. 

Fall plowing, relation to dry-farming, 

713. 
Fall and spring plowing, 283. 
Farm manures, 577. 
Farm manure, waste, 597. 
Fats in soil. 127. 
Fats, effect on capillarity, 211. 
Feeding power of plants, 414. 
Feldspar, as potash fertilizer, 524. 
I'cldspar in soil separates, 101. 
Fermentation, effect on pho.sphates, .520. 
Fermentation of manure, 591. 
I'^^rric phosphate availability, 337. 
I''crtilizers, 489. 
Fertilizers and acidity, 381. 

amounts to use, 572. 

application of, 570. 

brands, 555. 

catalj-tic, 530. 

commercial value, 560. 

commercial, extent of u.sc, 492. 

effect on toxic material, 137. 

factors in efficiency, 508. 

for special crops, 571. 

grades of, 562. 

home mixing, 563. 

incompatible material, 565. 



INDEX 



755 



Fertilizers, inspection, 5,56. 

mixed, 561. 

nitrogen, 493. 

penftratibn into soil, 354. 

practice, 546. 

potash, 522. 

systems of, 573. 

sulfur, 524. 

trade value, 559. 
Fertilizing crops, 571. 
Filler in fertilizer, 556. 
Filler in fertilizer, muck, 545. 
Film water, 206, 210. 
Fineness in phosphates, 513. 
Finger lakes, 50. 
Fire-fanging, manure, 596. 
First bottom land, 42. 
Fish as fertilizer, 50S. 
Floats to reinforce manure, 610. 
Flocculation, 159. 

Flooding, as means of soil infection, 425. 
Flooding, irrigation by, 699. 
Flume, for measurement of water, 707. 
Flushing, correction for alkali, 401. 
Food of animal, effect on manure, 582. 
Food elements, sources, 4. 
Food material in crops, 418. 
Food of plants, absorption of, 404. 
Forces of weathering, 14. 
Formic acid secreted by roots, 408. 
Forests and acidity, 380. 
Forest trees, niycorrhize of, 428. 
Free water in soil, 236. 
Free water, bad effects, 262. 
Freezing, efTeet on granulation, 189. 

relation to soil colloids, 166. 
Fresh versus leached manure, 601. 
Friction and available water, 256. 
Friction coefficient, 229. 
Frost as soil pulverizer, 680. 
Frost as weathering agent, 17. 
Frozen soil, bacteria in, 431. 
Fruiting effect of nitrogen, 548. 
Fruits, feeding power, 416. 
Functions of fertilizers, elements, .547, 
549, 551. 

of soil to plant, 1. 

of water to plant, 243. 
Fungi and fire-fanging of manure, 596. 
Fungi in soil, 423. 
Furrow, back, productive, 671. 

correct position, 668. 

dead, objectionable, 671. 

depth and width, 669. 

use in irrigation, 702. 
Fusarium as a disea.se organism, 426. 



Gabbro, 6. 

Gases, from manure, .594. 

Gel colloids, 159. 

Geological classification of soil material, 

31. 
Germination, effect of heat on, 290. 
Glacial drift, 47. 
Glacial ice, as erosive agent, 16. 
Glacial lakes, 55. 
Glacial soil, composition, 52. 
Glacial soil, humus in, 54. 
Glacial soils, 47. 
Glauconite, solubility, 339. 
Gneiss, 6. 

Grade of drains, 645. 
Grain, effect of phosphorus, 550 

effect of potassium, 551. 

effect of nitrogen, 548. 
Granite, 6, 8. 

weathering of, 27. 
Granular soil. 111. 
Granulation, 185. 
Granulation, cause of, 187. 

defined, 170. 

effect of plow, 195. 

effect on cohesion, 179. 
Granulation of soil and optimum mois- 
ture, 263. 

effect of drainage, 630. 

modified by tillage, 663. 
Granulabacter, group of bacteria, 464. 
Granules in soil, 109. 
Grass crops, feeding power, 415. 
Gravel, 99. 

Gravitational water, 201, 233. 
Gravitational water, injurious to crops, 
261. 

calculation of, 237. 

control of, drainage, 627. 

movement, factors affecting, 233, 
235. 

movement of, 233. 

study of, 238. 
Green manure, 151. 
Green manure, and acidity, 379. 

conditions for plowing under, 624. 

constituents added, 621. 

crops, 622. 

decay in soil, 622. 

denitrification, 547. 

effects, 619. 

lime relations, 625. 

relation to the rotation, 625. 
Ground limestone, 540. 
Ground water and capillarity, 214. 
Group, the, in soil classification, 723. 



756 



INDEX 



Growing season, effect of drainage, 6.31. 

Growth, efTect3 of nitrogen, 547. 

Guano, as fertilizer, 507. 

Guarantee, fertilizer, 558. 

Gypsum, 9, 542. 

Gypsum, correction for alkali, 400. 

Gyp.sum, lime fertilizer, 539. 

Gypsum, solvent action of roots on, 

406. 
Gypsum to reinforce manure, 609. 

Handling manure, 602. 

Hardpan, alkali, effect on drainage, 659. 

Harrow as cultivator, 676. 

Heat, absorption of, 300. 

and cold, mechanical action, 16. 

chemical and physical changes due 
to, 291. 

condensation, 209. 

convection in soil, 307. 

functions of, in soil, 289. 

effect on soil, 466. 

unit defined, 314. 

sources in soil, 292. 

specific heat of soil, 294. 
Head of water, defined, 706. 
Head of water for irrigation, 702. 
Heaving of soil indicates wetness, 628, 

632. 
Heiden's formula for manure production, 

588. 
Helminthosporium, disease organism, 

426. 
Hematite, 9. 

Hematite, hydration of, 21. 
Herring-bone system of drainage, 645. 
High-grade fertilizer, 562. 
Hillside plow, 670. 
Histidine, plant-food, 497. 
Home-mixing fertilizer, 563. 
Home-mixing fertilizer, method, 5t)7. 
Hoof meal as fertilizer, 507. 
Hornblende, 9. 

Hornblende in soil separates, 101. 
Horse manure, composition, 584. 
Humid and arid soils, 71. 
Humid climates, irrigation in, 6S9. 

soils, composition of, 72. 

soils, organic matter of, 146, 147. 
Humidity, effect on hygroscopicity. 2D7. 
Humus, absorption by, 365. 
Humus ash composition, 145. 

and conductivity, 310. 

and capillarity, 219. 

and efficiency of fertilizer, 569. 

and roots of plants, 127. 



Humus ar.d run-off, 269. 

and specific heat, 297. 

as plant-food, 49.5. 

composition of, 131. 

content of soils, 147. 

effect of drainage on formation, 632. 

effect on hygroscopicity, 204. 

effect on granulation, 190. 

effect on cohesion, 170. 

effects on soil, 150. 

estimation of, 142, 144. 

in glacial soil, 54. 

nature of, in soil, 130. 

specific gravity of, 113. 
Humus, defined, 130. 
Hydration as weathering agent, 20. 
Hydrochloric acid used in soil survey, 

728. 
Hydrochloric acid solution of soil, 329. 
Hydrochloric acid test for carbonates, 

388. 
Hydrogen, 4, 6. 

Hydrogen, from plant decay, 140. 
Hygroscopic coefficient, 257. 
Hygroscopic moisture, 201, 202. 
Hygroscopic moisture and plasticity, 
171. 

relation to colloids, 168. 

relation to plants, 256. 
Hygroscopicity, determination of, 208. 

Ice, as erosive agent, 16. 

Ice-formed soils, 52. 

Ice sheet, 47. 

Igneous soil-forming rocks, 6. 

Implements, tillage, 664. 

Infection by soil fungi, 425. 

Inoculation of soil for legumes, 460. 

Inorganic colloids, 158, 162. 

Insects in soil, 423. 

Inspection of fertilizers, 556. 

Interception losses in forests, 287. 

Iodine in ash of sea weed, 404. 

Iron, 4, 6. 

Iron a catalytic fertilizer, 529. 

Iron as a soil color, 75. 

Iron pho.sphate available, 337. 

Iron in soil separates, 102. 

Irrigation, amount of water applied, 708. 

amount of water to apply, 710. 

and alkali, 397. 

application of water and yield, 208. 

canals, 693. 

canals, linings, 694. 

conditions that warrant, 683. 

development in the United States, 686. 



INDEX 



757 



Irrigation, erosion in canals, 694. 
flooding, 699. 
furrow, 702. 
history, 685. 
in humid regions, 689. 
legal, economic and social effects, 

691. 
land, drainage of, 659. 
land, extent of, 685. 
methods of water supply, 688. 
methods of applying water, 695. 
movement of water, 704. 
preparation of land, 695. 
relation to rainfall, 682. 
setting of fruit, 709. 
sewage, 711. 
sources of water, 693. 
sub, 696. 

theory and practice, 682. 
units of water measurement, 706. 

Jointer, 672. 

Joints, protection in tile drains, 642. 

Kainit, potassium salt, 522. 
Kainit to reinforce manure, 609. 
Karnes, 50. 

Kaolin, specific heat, 299. 
Kaolinite, 9. 

Lacustrine soils, 56. 

Lagoons, 40. 

Land drainage, indications of need, 627. 

Land plaster, 542. 

Land plaster to reinforce manure, 609. 

Leaching of manure, 599. 

Leather meal as fertilizer, 507. 

Legumes and symbiosis, 458. 

Legumes, feeding power, 415. 

Legume manure, nitrogen added by, 

621. 
Leguminous green manures, 623. 
Lento-capillarity, 2.57. 
Lento-capillarity, defined, 224. 
Leucite, solubility, 339. 
Level tillage, 286. 
Lime as amendment, effects, 534. 
Lime carbonate, 333. 
Lime, a catalytic fertilizer, 528. 

effect on bacteria, 432, 436. 

effect on nitrates, 536. 

effect on toxic substances, 536. 

effect on efficiency of fertilizer, 509. 

effect on sanitation of soil, 138. 

effect on graniilation, 193. 

fertilizer mixtures of, 566. 



Lime, flocculating agent, 160. 

forms of, 539. 

formation of humus, 152. 

green manure and, 625. 

loss in drainage, 372. 

manure and, 612. 

nitrogen fi.Kations, 464. 

relation to available pho.sphorus, 
517. 

relation to soil colloids, 166. 

relation to soil diseases, 426. 

run-off relationships, 209. 

soil separate content, 101. 

soil and subsoil content, 378. 
Lime-magnesia ratio, 538. 
Lime phosphate, effect of bacteria on, 

439. 
Limestone, 6, 8. 
Limestone for soil, 539. 
Limestone, residual soil from, 33. 
Limestone soil, not rich in lime, 28. 
Limestone, weathering of, 27. 
Limewater test for acidity, 390. 
Limonite, 9. 

Linseed meal as fertilizer, 507. 
Liquid manure compared with solid, 585. 
Lister, seeder cultivator, 678. 
Listing, effect on soil ventilation, 487. 
Lysimeter described, 239. 
Litmus test for acidity, 386. 
Litter, absorptive capacity, 603. 
Litter in manure, 578, 580. 
Loam, defined, 104. 
Loess, ^olian soil, 58. 

description and composition, 59. 

wind origin, 15. 

soil distribution of, 51. 
Loss of manure in handling, .583, 600. 
Low-grade fertilizer, 562. 

Machinery, tillage, 664. 
Macroorganisms in soil, 421. 
Macrosporium, disease organism in soil, 

426. 
Magnesium, 4, 6 
Magnesium carbonate, and nitrates, 536. 

catalytic fertilizer, 530. 

in soil separates, 102. 
Manure, 489. 

Manure, amount produced by animals, 
587. 

commercial value, 589. 

composition, causes of variation, 580. 

composition of gases from, 594. 

composition of rotted, 596. 

composting, 613. 



758 



INDEX 



Manure, covered yard? and pits, 605. 

denitrification of, 457. 

destruction of organic matter in 
feed, 597. 

effect of food of animal, 582. 

effect of handling on composition, 
583, 600. 

effects on the soil, 613. 

effect on soil ventilation, 488. 

farm, 597. 

farm corrects alkali, 403. 

fermentation, 591. 

frequent small applications, 007. 

fresh versus leached, 601. 

fire-fanging, 596. 

functions, 489. 

green, 619. 

green and lime, 625. 

Heidens formula for production, 588. 

lime and, 012. 

muck and, 613. 

needs and plant food deficiency, 334. 

organic and nitrification, 450. 

plowing under, 608. 

reinforcement, 609. 

residual efTects, 614. 

rotation relation, 615. 

small versus large applications, 608. 

spreader, 608. 

storage in open piles, 606. 

yard composition, 578. 
Marble, 6, 43. 

Marine soil compositions, 66. 
Marl, 539. 
Marl, composition, 38. 

found under muck, 37. 
Marsh mud composition, 37. 
Maturity, effect of nitrogen, 548. 
Maturity, effect of phosphorus, 550. 
Maximum water content, 262. 
Measurement of water in irrigation, 706. 
Meat, as fertilizer, 507. 
Mechanical analysis, 84. 
Mechanical analysis of samples, 728. 
Meeker harrow, 677. 
Metamorphic soil-forming rocks, 6. 
Methane in soil air, 140. 
Mica in soil separates, 101. 
Microcline, solubility, 338. 
Microorganisms, 424. 
Microorganisms, effect of sulfur, 525. 
Mineral acid, method of analysis, 338. 

colloids, 162. 

definition of, 7. 

matter, decomposition by bacteria, 
437. 



Mineral acid, nutrients of feed in ma- 
nure, 507. 

pho.'sphates as fertilizer, 512. 
Minerals, absorbed by plants, 416. 

law of deca.v, 24. 

relative abundance, 11. 

rock-forming, 8. 

soil-forming, 8. 
Mineralogical character of soil separates, 

99. 
Miner's inch of water, defined, 706. 
Minimum, law of, 551. 
Mississippi River, denudation by, 15. 
Mixed fertilizers, 561. 
Modification of structure, 187. 
Module, for measuring water, 709. 
Moisture of the soil, 198. 

conductivity relations, 310. 

capacity of soil, effect of drainage, 
631. 

capillary form, 210. 

conservation in irrigation, 710. 

content, effect on soil air, 476. 

control of, 264. 

effect on bacteria, 434. 

effect on cohesion, 179. 

effect of movement on soil air, 484. 

equivalents of soil, 220. 

forms of, 200. 

gravitational, 233. 

hygroscopic, 202. 

maximum content, 221. 

methods of stating, 198. 

relation to colloids, 165. 

relation to decay, 129. 

relation to plowing, 196. 

used by plant, 261. 

uses to plant, 243. 
Moldboard plows, 667. 
Moldboard, shapes for best result, 

196. 
Molds in soil, ammonify proteins, 427. 
Mole drainage, 638. 
Moraine, terminal, 50. 
Movement, of soil air, 483. 

heat, 307. 

heat factors affecting, 308, 310. 

moisture, capillary, 221. 

moisture, factors affecting capillarity, 
223. 

moisture, gravitational, 233. 

moisture, thermal, 241. 

water, affected by friction, 223. 

water, affected by texture, 229. 

water, affected by structure, 232. 
Muck, defined, 36. 



INDEX 



759 



Muck, as fertilizer, 545. 

and manure, 613. 

and moisture control, 272. 

nitrogen compounds in, 13.3. 

specific growth of, 113. 
Mulch and the control of alkali, 402. 
Mulch, depth of, 278. 

depth in irrigation farming, 705, 715, 

dry-farming, use in, 714. 

effectiveness in arid regions, 277. 

effect other than on moisture, 280. 

factors of effectiveness, 275. 

formation of, 276. 

functions of, 274. 

kinds of, 273. 

management of, 278. 

of soil, 233. 

r68um6 of control, 278. 

usefulness of, 282. 

water saved by, 279. 
Mulching grain crops, 282. 
Muriatic acid used in soil survey, 728. 
Muscovite, 9. 
Muscovite, solubility, 339. 
Mycorrhiza, relation to fertility, 423. 
Mycotrophic plants, 423. 

Natural mulch, 273. 
Negative acidity, 376. 
Nematodes in soil, 424. 
Nephelite, solubility, 339. 
Nitrate assimilation by bacteria, 456. 
Nitrate of calcium, fertilizer, 505. 
Nitrate of soda, as plant food, 498. 
Nitrate, reduction of, 455. 
Nitrates, conserved by green manure, 
620. 

constituent of alkali, 392. 

effect of lime on, 536. 

in soil, effect of absorption on, 341. 

lo.ss from soil, 4.54. 

product of decay proces.ses, 130. 

returned to surface, 454. 
Nitric acid method of analysis, 338. 
Nitric acid solution of soil, 329. 
Nitrification in soil, 447. 

effect of aeration, 452. 

effect of antiseptics, 465. 

effect of carbon bisulfide, 466. 

effect of depth, 453. 

effect of organic matter, 449. 

effect of sod, 452. 

temperature for, 435. 
Nitrobacter in soil, 448. 
Nitrogen, 4, 12. 

absorption of, 367. 



Nitrogen, added to .soil by legumes, 621. 

available from atmosphere, 501. 

chemical estimation, 329. 

cycle, 443. 

effects on plant growth, 547. 

effect on toxic material, 137. 

fertilizers, 493. 

fertilizer from the air, 501. 

fertilizers, organic, .507. 

fixation, 457. 

fixation and mycorrhiza, 428. 

fixation by molds, 427. 

fixation, non-symbiotic, 463. 

fixing organisms, 463. 

forms in soil, 493. 

forms used by plants, 448, 494. 

found in animal manures, 597. 

in humus, 147. 

loss in drainage, 372. 

loss from Rothamsted soil, 500. 

necessary to plants, early studies, 
491. 

supply and bacteria, 428. 

utilized by bacteria, 459. 
"Nitrogen" culture, 461. 
Nitrosococcus in .soil, 448. 
Nitrosomonas in soil, 448. 
Nodules on plant roots, 458. 
Number of soil particles, 118. 
Nutrient salts, absorption of, by plants, 
404. 

absorption by soils, 349. 

selective absorption, 362. 

Odometer used in soil survey, 727. 

Oils, effect on capillarity, 214. 

Oils in soil, 128. 

Oily material, and capillary movement, 

226, 228. 
Oily materials in soil, 275. 
Olivine, 9. 

Open ditches, construction, 635. 
Open-ditch drainage, objections, 634. 
Optimum water content, 262. 
Orchards, manure in, 617. 
Organic colloids, 157, 161. 
Organic fertilizer availability, 510. 
Organic constituents of soils, 2, 12, 128, 

131. 
Organic decay and .soil temperature, 315. 
Organic matter, 12. 

absorption by, 365. 

and capillary water, 218. 

catalytic action, 529. 

composition in .soil, 135. 

effect on granulation, 190. 



760 



INDEX 



Organic matter, effoct on nitrification, 
449. 

effect on phosphates, 520. 

effects on .soil, 150. 

effect on soil bacteria, 435. 

efficiency of fertilizer, 569. 

estimation of, 141. 

losses in digesting food, 597. 

maintenance in soil, 151. 

relation to air in soil, 476. 

soil content, 126. 

soils of U. S. content, 146. 

source of carbon dioxide, 479. 

specific heat relations, 297. 
Organic nitrogen, plant food, 497. 
Organisms in soil, 421. 

effect of heat on, 289. 

effect of drainage on, 632. 

macro- in soil, 421. 

micro- in soil, 424. 
Orthoclase mineral, 9. 

solubility of, 338. 

weathering of, 22. 
Osmotic activity of plant roots, 412. 
Outlets to the drains, 656. 
Oxbows, 40. 

Oxidation and soil fertility, 137. 
Oxidation as weathering agent, 19. 
Oxidation of sulfur in soil, 525. 
Oxygen, 4, 6. 

Oxygen, absorption of, 367. 
Oxygen, effect on soil bacteria, 433. 
O.Kygen in soil, air functions, 480. 
Oxygen in soil, relation to carbon dioxide, 
479. 

Packers and crushers, 678. 
Packer, sub-surface, 679. 
Partial solution of soil, 329, 331. 
Particles, in soil, chemical composition, 
101. 

in soil, mineral composition, 09. 

in .soil, physical character, 98. 

of soil, classification, 95. 

of soil, number, 118. 

surface exposed in soil by, 120. 
Peas, materials used as food, 496. 
Peat, defined, 36. 
Peat, nitrogen compounds in, 133. 
Peat, specific gravit.v of, 113. 
Penicillium glaucum in soil, 427. 
Percolation of water, 233. 

effect of pressure on, 233. 

effect of texture and .structure on, 
235. 

effect on air movement, 483. 



Percolation of water, losses from, 265. 

losses from, control, 267. 

objection to, in irrigation, 704. 

llothamsted figures on, 266. 
Peridotite, 8. 

Permutite, absorption by, 357. 
Peruvian guano, 508. 
Phillipsite, .solubility, 339. 
Phosphate, acid, to reinforce manure, 010. 

bone, early manufacture, 492. 

calcium, root action on, 406. 

effect of bacteria on, 439, 437. 

fertilizers, 511. 

fertilizers, relative availability, 516. 

insoluble, 358. 

of iron and aluminum, 337. 

row rock, to reinforce manure, 610. 

relation to carbon dioxide, 482. 

reverted, 515. 
Phosporic acid, absorption of, 352, 357. 
Phosphorite as fertilizer, 512. 
Phosphorus in soil, 4, 6. 

effect on toxic materi.-vl, 137. 

effects on plant growth, 549. 

in soil separates, 101. 
Physical agencies of weathering, 14. 

absorption, 359. 

changes due to heat, 291. 

character of soil separates, 98. 

effect of organic matter, 150. 
Piedmont soils, 34. 
Plagioclase, 9. 

Plane (able for soil survey, 727. 
Planker, .as soil pulverizer, 680. 
Plant food, elements of, in soil, 3. 
Plant food, deficiencies and manurial 
needs, 334. 

distribution in liquid and solid ma- 
nure, 580. 

elements, abundance of, 5. 

elements, essential, 417. 

elements, sources of, 4. 

appearing in manure, 597. 

in soil minerals, 101. 

in plants, 418. 

limiting elements, 4. 

proportion of feed in manure, 581. 

relation to bacteria, 428. 

relation to dilution, 332. 

shown by analysis, 330. 

supplied in sewage, 711. 
Plant growth, effects of nitrogen, 547. 

factors for, 3. 

functions of water, 243. 

and the soil solution, 347. 

and strength of soil solution, 417. 



INDEX 



761 



Plant nutrients, absorption of, 404. 
Plant roots in soil, 424. 
Plant roots, solvent action, 405. 
Plants, absorptive power, 412. 

acid in juices, 379. 

available water for, 261. 

composition of, 128. 

effect of alkali on, 394. 

effect on availability of pho.sphorus, 
518. 

effect on granulation, 192. 

indicating an acid soil, 382. 

requirements for growth, 3. 

soil-forming agents, 18. 

soil shelters, 287. 

succession on soil, 1. 

utilize simple and complex material, 
131. 

water requirements of, 244. 
Plasticity, causes of, 172. 
Plasticity, defined, 170. 
Plow attachments, 671. 

effect on granulation, 195. 

hillside, 670. 

as tillage implement, 665. 

subsoil, 672. 

sale of, 670. 
Plowing, correct position of furrow, 668. 

depth, 609. 

fall, relation to dry-farming, 713. 

under manure, 608. 
Poncelet's formula, 652. 
Pore space in spherical particles, 109. 

in soil, 115. 

in soil, calculation, 116. 
Porosity and diffusion of gases, 483. 
Positive acidity, 375. 
Potassium in soils, 4, 6. 

absorption of, 358. 

chloride, .523. 

effects on plant growth, 551. 

effect on toxic material, 137. 

fertilizers, 522. 

nitrate test for acidity, 388, 389. 

soil separates content, 101. 

solubility, 339. 

sulfate, 523. 
Poultry manure, composition, 582, 588. 
Pressure, atmospheric, affects soil air, 

484. 
Properties of soil separates, 98, 99, 101. 
Protein decay, 447. 
Proteins in soil, 127. 

Protozoa, relation to soil productive- 
ness, 471. 
Province, the, in soil classification, 723. 



Puddled soil, 110. 

Pulverizing action of plow, 195, 665. 
Putrefaction and decay, 443. 
Putrefaction, products of, 445. 

Quartz, mineral, 9. 
Quartz, specific heat, 299. 
Quartz, in soil separates, 99. 
Quartzite, 6. 
Quicklime, 539. 

Quicksand, management in drainage, 
660. 

Radiation, effect of moisture, 305. 

Radiation from soil, .302. 

Rainfall, distribution in world, 683, 686. 

effect on soil ventilation, 483. 

relation to irrigation, 682. 
Raw rock phosphate, 512. 
Reclamation service of the United 

States, 688, 690. 
Reconnoissance soil surveys, 737. 
Reduction of nitrates, 455. 
Reinforcement of manure, 009. 
Residual effects of manure, 614. 
Residual soils, colors, 33. 

characters of, 32. 

composition of, 60. 

defined, 31. 

distribution of, 34. 

origin of, .31. 
Resinous material in soil, 275. 
Reverted phosphate, 515. 
Ridge tillage versus level, 287. 
Riparian rights, modified under irriga- 
tion, 691. 
Ripening and moisture, 253. 
Rodents in soil, 421. 
Rock flour, 68. 
Rock rot, 68. 
Rock-forming minerals, 8. 
Rock, definition of, 7. 
Rocks, acid, 7. 

basic, 7. 

classification of, 6. 

coefficients of expansion, 17. 

decay agencies of, 14. 

law of decay, 24. 

soil-forming, 6. 

solubility in sodium carbonate, 20. 

weathering of, 13. 
Rolling and moisture control, 284. 
Roller as soil pulverizer, 679. 
Root crops, feeding power, 415. 
Root-hairs and food absorption, 404. 
Root-hairs, relation to soil particles, 405. 



762 



INDEX 



Root development, effect of drainage, 

G31. 
Root excretions, 136. 
Roots, effect on colloids, 411. 
effect of phosphorus, 550. 
effect on soil ventilation, 488. 
entrance into tile, (542. 
extent of surface, 412. 
nodules on, 458. 
of plants, distribution, 81. 
of plants and humus, 127. 
of plants under dry-farming, 717. 
of plants in soil, 424. 
oxidizing enzymes in, 407. 
solvent action, 405. 
Rotation and green manure, 625. 

of crops and maintenance of humus, 

152. 
of crops and manure, 615. 
of crops, remedy for soil diseases, 
425. 
Rothamsted, composition of drainage 
water, 370. 
drain gauges, 20G. 
losses of nitrogen, 500. 
Run-off, losses from, 265. 

Salt, as amendment, 543. 
Sampling soil in the field, 731. 
Sand, 99. 
Sand dunes, 63. 
Sandstone, 6, 8. 

Sanitation of soil, effect of drainage, 633. 
Sanitation of soil and toxic material, 137. 
Saturated soil, 201. 
Sawdust as litter, 603. 
Schist, 6. 

Scraping, correction for alkali, 401. 
Second-food of water, defined, 706. 
Sediment in water, effect on erosion, 637. 
Sedimentary, soil-forming rocks, 6. 
Seeding machines as cultivators, 678. 
Seepage, extent and prevention in irri- 
gation, 694. 
Selective absorption, 362. 
Selective absorption by colloids, 165. 
Separates, mineralogical character, 99. 
Separates, physical character of, 98. 
Separates of soil, 84. 
Series, the, in soil classification, 722. 
Series of soil, named, 725. 
Serpentine, 9. 
Sewage irrigation, 711. 
Sewage-sick soil, 474. 
Shading and moisture loss, 287. 
Shale, G. 



Sheep manure, composition, 584. 
Shelters and moisture control, 285. 
Siderite, 9. 

Silica in soil separates, 102. 
Silicates, absorption by, 360. 
Silicates, influence on absorption, 357. 
Silicon, 6. 

Silt, character of separate, 98. 
Silt-basins, in drains, 656. 
Silvinit, potassium salt, 523. 
Single-grain structure, 110. 
Size of colloidal particles, 154. 
Size of soil particles, 95. 
Size of the drains, 650, 654. 
Slate, 6. 

Slag phosphate, 513. 
Slope and temperature, 317. 
Slime molds in soil, 425. 
Snow, effect on soil temperature, 306. 
Sod, effect on nitrification, 452. 
Sodium, 6. 

Sodium compounds, as fertilizer, 544. 
Sodium nitrate, as plant food, 498. 
Sol, colloidal condition, 159. 
Soldate, module, 707. 
Solid manure compared with liquid, 585. 
Solubility of rocks in sodium carbonate, 
26. 

of soil and texture, 331. 

of the soil, 327. 
Solution and soil formation, 21. 
Solution in soil and plant growth, 417. 
Solvent action of roots, 405. 
Solvents of the soil, 328. 
Soil amendments, 534. 

best suited for dry-farming, 716. 

classification, factors used, 720. 

composition, general, 2. 

defined, 1. 

organic matter, 126. 

organisms, 421. 

sampling in the field, 731. 

solution in situ, 342. 

solution and plant growth, 347. 

survey, accuracy and detail, 733. 

survey, equipment for, 726. 

surveys, extent, 737. 

survey map, 736. 

survey report, 735. 

survey, its uses, 739. 

survey, principles of classification, 
718. 

tjTJe, name, 725. 
Soil and subsoil, arid and humid regions, 

82. 
Soil and subsoil, defined, 79. 



INDEX 



763 



Soil-forming minerals, 8. 

Soil-forming rooks, G. 

Soil mulch versus dust mulch, 275. 

Sour soils, 37o. 

Sources of plant food, 419. 

Specific gravity, absolute, 112. 

apparent, 113. 

of minerals, 112. 

of soil separates, 113. 
Specific heat of soil, 294. 
Spray system of irrigation, 695. 
Spring, early plowing, 283. 
Stall manure versus yard manure, 601. 
Starch, effect of potassium, 551. 
Stassfurt salts, 522. 
Storage of water in soil, 279. 
Straw, effect of nitrogen, 548. 

effect of phosphorus, 550. 

relation to denitrification, 456. 
Stone drains, 638. 
Stone mulch, 273. 
Structure and capillary movement, 232. 

and capillary water, 217. 

and conductivity, 310. 

defined, 108, 170. 

effect on diffu.sion of gases, 483. 

effect on gravitational movement, 235. 

modified by tillage, 663. 

relation to air in soil, 476. 

temperature relations, 304. 
Subirrigation, 696. 
Subsoil and soil defined, 79. 
Subsoil, composition of, 332. 
Subsoil plow, ()72. 

Subsoiling, relation to dry-farming, 713. 
Substitution of bases, 355. 
Substitution of elements by plant, 417. 
Subsurface packer, 679. 
Subsurface packing, 714. 
Sulfates as fertilizer, 526. 
Sulfate of ammonia as fertilizer, 499. 
Sulfate of potash, 523. 
Sulfur, 4, 6. 

Sulfur and acidity, 382. 
Sulfur as fertilizer, 524. 
Sulfur bacterin in soil, 439. 
Sulfur dioxide, from plant decay, 140. 
Sulfur, free, as fertilizer, 524. 
Sulfuric acid solution of soil, 329. 
Superphosphate fertilizer, 514. 
Surface of roots, 412. 
Surface of soil particles, 120. 
Surface tension, 211. 

and capillary movement, 227. 

and capillary water, 213. 
Surface water, composition of, 373. 



Swine manure, composition, 584. 
Symbiosis, nitrogen fixation through, 

457. 
Syenite, 6, 8. 
Systems of fertilization, 573. 

Talc, 9. 

Tankage as fertilizer, 507. 
Temperature changes, affect soil air, 484. 
Temperature in fermenting manure, 593. 
Temperature of soil and air, 485. 

annual, 321. 

annual range, 322. 

control, 325. 

daily range, 324. 

effect of drainage, 631. 

effect of slope, 317. 

effect of snow, 306. 

evaporation influence, 314. 

factors affecting, 293. 

influence on absorption, 367. 

influence on bacterial activity, 435. 

influence on efficiency of fertilizer, 
568. 

influence decay, 129. 

influence on hygroscopicity, 207. 

influence on movement of water, 234. 

influence on organic decay, 315. 
Tenacity of soil, 174. 
Terrace, defined, 41. 
Texture, adaptation of crops to, 105. 

defined, 83. 

effect on capillary movement, 214, 
229. 

effect on cohesion, 179. 

effect on conductivity, 308. 

effect on hygroscopicity, 204. 

relation to air in soil, 475. 

relation to gravitational movement, 
235. 

relation to soil classification, 722. 

relation to solubility of soil, 331. 

relation to wilting point, 260. 

rock, and weathering, 23. 

influence on absorption, 355. 

influence on diffusion of gases, 483. 

temperature relations, 304. 
Thermal movement of water, 241. 
Tile, quality, 640. 
Tile drains, 639. 

carrying capacity, 651. 

cost, 654. 

dangers from roots, 642. 

depth, 646. 

formula for size of tile, 652. 

grade, 645. 



764 



INDEX 



Tile drains, interval, 647. 

laying, 649. 

outlets, 656. 

silt basins, 656. 

size, 650, 654. 

surface intakes, 656. 

trenches, construction, 648. 
Tile drainage in alkali land, 659. 
Tile drainage in muck and peat soil, 658. 
Till, glacial soil, 53. 
Tillage, objects, 663. 

relation to colloids, 166. 

relation on granulation, 194. 

relation to means of soil infection, 
425. 

relation to run-off, 269. 

relation to soil ventilation, 487. 

implements, 664. 

practices, 663. 
Tillering and moisture, 253. 
Tilth, effect of lime, 534. 
Tilth of soil, 184. 

Toxic material and drainage, 262, 632. 
Toxic material in soil, 136. 
Toxic substances, effect of lime, 536. 
Toxicity and loss of bases, 378. 
Trade values of fertilizer, 559. 
Transpiration ratio, 244. 
Transpiration and fertility, 2.50. 
Transported soils, 31, 46. 
Type of soil, named, 725. 
TjTse of soil, the unit, 720. 

Unavailable soil water, 256. 
Underdrains, advantages, 635. 
Underdrains, tile, 639. 
Units in water measurement, 706. 
Urea, derived from cyanamide, 504. 
Urea, product of decay, 130. 
Urine in manures, 584, 586. 

Value of fertilizer, trade, 559, 562. 

Value of manure, commercial, 602. 

Vegetables, feeding power, 415. 

Vegetation as means of soil classifica- 
tion, 720. 

Vegetative growth, favored by nitrogen, 
547. 

Ventilation of soil, effect of drainage, 
487, 630. 

Vertical drainage, 660. 

Volcanic dust, 63. 

Water, amount to apply in irrigation, 710. 
available to plants, 261. 
application, time, 709. 



Water, as solvent in soil analysis, 340. 

as weathering agent, 14. 

carrying power, 40. 

content, maximum, 262. 

control of, 264. 

capillary form, 210. 

effect of movement on soil air, 483. 

equivalents of soil, 220. 

expansive power in freezing, 17. 

forms in soil, 200. 

functions of, in plant growth, 243. 

gravitational form, 233. 

hygroscopic form, 202. 

interception loss(?s, 287. 

losses from evaporation, 270. 

losses from run-off, 265. 

relation of application to yield, 708. 

requirements of plants, 244. 

saved by mulch, 279. 

sources for irrigation, 693. 

specific heat, relation to, 298. 

storage in soil, 713. 

surfaces in soil, 212. 

unavailable in soil, 256. 
Water-logged land, 6.59. 
Water-slaked lime, 539. 
Weathering, conditions affecting, 22. 

forces of, 14. 

in arid and humid regions, 23. 

of rocks, 13. 

special cases, 27. 
Weeder, cultivator, 676. 
Weeds and crop growth, 280. 
Weight of soil, 115. 
Weir, for measurement of water, 707. 
Wetting and drying, effect on granula- 
tion, 187. 
White alkali, 392. 
Wilt of crops, a soil organism, 425. 
Wilting coefficient, 257, 2.">8. 
Wilting point, calculation of, 260. 
Wilting point, relation to texture, 261. 
Wilting, when it occurs, 257. 
Wind, effect of suction on soil air, 486. 
Wind, erosion by, 15. 
Wind, .soils formed by, 58. 
Wind-breaks and moisture control, 285. 
Wood ashes, as fertilizer, 523. 
Wool waste, as fertilizer, 507. 
Worms in soil, 422. 

Yard manure, 578. 

Zeolites, 9, 355. 

Zinc sulfide test for acidity, 387. 

Zircon, 9. 



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half-tones, thereby giving an artistic appearance to the volume. 

Plant-Breeding 

By L. H. bailey. New Edition 

Revised by A. W. GILBERT, Professor of Plant-Breeding in the New York State 
College of Agriculture 

Illustrated, cloth, i2mo, $2.00 
The original foundation for this book is Professor Bailey's standard 
text, Plant-Breeding, first published in 1895. As now issued the 
material in the old volume has been thoroughly revised and brouglit 
down to date. New discussions of nuitations, Mendelism, heredity and 
the recent applications of the breeding of plants are all included. 
The work is now adapted to the classroom as well as to the needs of 
the general reader. Extensive laboratoiy exercises have been adiled ; 
the bibliography, which has been a prominent feature of previous edi- 
tions, except the first, has been retained and extended. A list of cur- 
vent books and periodicals and a glossary of plant-breeding terms are 
also contained in the book. 



THE MACMILLAN COMPANY 

PubliBhers 64-66 Fifth Avenue New York 



The Standard Cyclopedia of Horticulture 

Edited by L. H. BAILEY 

With the Assistance of over 500 Collaborators 

New edition, entirely rewritten and enlarged, with many new features ; 

with 24 plates in color, g6 full-page half-tones and 

over 4,000 text illustrations 

To be complete in six volumes Sold only in sets by subscription 



The Country Gentleman's Companion The Gardener's Manual 
The Amateur's Guide The Student's Textbook 

The Botanist's Treasure The Teacher's Library 



This, the fullest, the newest, the most authoritative of all works 
of its kind, supersedes the old Cyclopedia of American Horticulture 
first issued fourteen years ago. '* The Standard Cyclopedia of Hor- 
ticulture" is an entirely new work, freshly written throughout with 
the assistance of 500 collaborators. It represents the most recent 
research, labor and experience, and compresses the whole story of 
thought, learning, and achievement on the subject into one set of 
six large, handsome quarto volumes. 



TWO OPINIONS OF THE NEW CYCLOPEDIA 

" No one who knows anything at all about the literature of gar- 
dening needs to be told that the Cyclopedia is unique. It is the 
Bible and Britannica of the garden-folk, amateur and professional 
alike. And the remarkable thing is that while it is fundamentally a 
work of reference, it also contains limitless quantities of good read- 
ing of the sort dear to the heart of the garden enthusiast." — The 
Nation. 

" It is no exaggeration to state that Bailey's new work is the best 
Cyclopedia obtainable for all who are connected, either remotely or 
intimately, as amateurs or professionals, with horticultural pursuits." 
— The Florists'' Review. 

THE MACMILLAN COMPANY 

Publishers 64-66 Fifth Avenue New York 



Electricity for the Farm 

LIGHT, HEAT, AND POWER BY INEXPENSIVE METHODS 
FROM THE WATER WHEEL OR FARM ENGINE 

By FREDERICK IRVING ANDERSON 

Author of " The Farmer of To-morrow " 
Cloth, i2mo, illustrated, $i.2§ 

A year or so ago there was published an exceedingly 
practical little work entitled " The Farmer of To-morrow.'* 
Rarely has as much of genuine value been put into a book 
as was put into this one, and the author, Frederick Irving 
Anderson, was looked to for further contributions in the 
same field. The announcement, therefore, of the appear- 
ance of " Electricity for the Farm " will be welcomed by all 
farmers and students of agricultural matters. 

Mr. Anderson believes that many farmers are not mak- 
ing the most of their opportunities. He shows how, with 
very little expense, a farmer may have all the benefits of 
electricity for light, heat, and power either by installing a 
simple gasoline engine or by using the neglected brook that 
runs through some part of the farm lands. As he points 
out, a mighty stream is not necessary to secure sufficient 
power, but a rivulet with only a little fall will quite answer 
the purpose. Realizing, however, that not every farm has 
even "a babbling brook," he considers other sources of 
power. 

THE MACMILLAN COMPANY 

Publishera 64-66 Fifth Avenue New Tork 



